National Highway
Traffic Safety
Administration



DOT HS 809 023June 1999












Evaluating Drivers Licensed with
Medical Conditions in Utah, 1992 1996




















This document is available to the public from the National Technical Information Service, Springfield, Virginia 22161.









Technical Report Documentation Page

1. Report No.  DOT HS 809 023

2. Government Accession No.

3. Recipients's Catalog No.


4. Title and Subtitle

Evaluating Drivers Licensed with Medical Conditions in Utah, 1992 1996

5. Report Date

June 1999

6. Performing Organization Code

  1. Author(s) E. Diller, L. Cook, D. Leonard,

J. Reading, J. M. Dean and D. Vernon

8. Performing Organization Report No.

9. Performing Organization Name and Address

Utah CODES
410 Chipeta Way, Suite 222
Salt Lake City, UT 84108

10. Work Unit No. (TRAIS)n code


11. Contract of Grant No.

DTNH22-96-H-59017 Modification 0002

12. Sponsoring Agency Name and Address

U.S. Department of Transportation
National Highway Traffic Safety Administration
400 Seventh Street, SW
Washington, DC 20590

13. Type of Report and Period Covered

NHTSA Technical Report, 1992 1996

14. Sponsoring Agency Code


15. Supplementary Notes

16. Abstract

The Utah Driver License Division has implemented a program since 1979 that restricts drivers with medical conditions by functional ability category (medical condition) according to their functional ability level. This study compares the citation, all crash, and at-fault crash rates per eligible licensed days of restricted and unrestricted drivers with medical conditions by category to the rates of comparison drivers matched on age group, gender and county of residence over a five year period. Analyses were performed separately for drivers reporting single medical conditions and those reporting multiple medical conditions. Probabilistic linkage was used to link data from different databases in order to determine the crash, at fault crash and citation rates by functional ability restriction classification at the time of occurrence. Corresponding relative risks and confidence intervals were calculated.

Overall, for most functional ability categories, unrestricted drivers with medical conditions as identified through the existing program had higher crash and at-fault crash rates compared to their corresponding comparison groups. For unrestricted drivers, the highest risk of at-fault crash was found in the learning, memory and communications category where the risk of at-fault crash was 3.63 times higher than their respective comparison group (95% CI 2.00, 6.60). The greatest differences in at-fault crash rates were found in several restricted license categories. Restricted drivers in the musculoskelatal abnormality or chronic medical disability group had a rate 11.29 times higher than their comparison drivers (95% CI 2.39, 53.25). Restricted drivers in the alcohol and other drugs category had an at-fault crash rate that was 5.75 times higher than their respective comparison group (95% CI 2.26, 14.61). Further evaluation of the crash and citation rates at specific functional ability levels, and crash environments by category, may provide indications for changing the levels at which restrictions are applied, or provide indications for new or additional types of restrictions to reduce crashes and citations in these populations.

17. Key Words functional motor ability, medical conditions, drivers, crash, citation, diabetes, epilepsy, cardiovascular, pulmonary, alcohol, vision, elderly, probabilistic linkage, CODES

18. Distribution Statement

Document is available to the public through the National Technical Information Service, Springfield, VA 22161

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No of Pages

22. Price

Form DOT F1700.7 (8-72)            Reproduction of completed page authorized











TABLE OF CONTENTS

Executive Summary

Introduction

State of Utah Functional Ability in Driving: Guidelines and Standards for Health Care Professionals

The Utah Crash Outcome Data Evaluation System

Evaluating the Existing Program of Licensing Drivers with Medical Conditions in Utah

OBJECTIVES

METHODOLOGY

Probabilistic Linkage

Comparison Driver Selection

RESULTS

Diabetes mellitus and other metabolic conditions

Cardiovascular conditions

Pulmonary conditions

Neurological conditions

Epilepsy and other episodic conditions

Learning, memory and communication

Psychiatric or emotional conditions

Alcohol and other drugs

Visual acuity

Musculoskelatal abnormality or chronic medical debility

Functional motor impairment

Drivers licensed in multiple functional ability categories

Comparing drivers with a single restriction status to drivers whose restriction status fluctuated during the study period

DISCUSSION

RECOMMENDATIONS

REFERENCES

Appendix A. State of Utah Functional Ability in Driving: Guidelines and Standards for Health Care Professionals

Appendix B. General Screening Questionnaire and Health Care Professional Forms

Appendix C. Matching Programs: Crash to License and Death Certificate to License

Appendix D. Drivers by Functional Ability Category, Age Group, Sex and Restriction Status
















Executive Summary

The Utah Driver License Division operates a specialized licensing program for drivers who have medical conditions. The program was developed by the division under the guidance of the Utah Medical Advisory Board. The program's guideline describes the physical, mental and emotional capabilities appropriate for various types of driving and determines license eligibility by medical condition or functional ability category, and functional ability level (1-12). The intent of the board was to create the least restrictive program possible that was consistent with public safety. Drivers who are licensed with medical conditions may receive a full unrestricted or restricted license depending on their functional ability level. Restricted licenses may include speed, area and/or time of day limitations. The functional ability or medical condition categories include:

  1. diabetes mellitus and other metabolic conditions,
  2. cardiovascular,
  3. pulmonary,
  4. neurologic,
  5. epilepsy and other episodic conditions,
  6. learning/memory/communications,
  7. psychiatric or emotional conditions,
  8. alcohol and other drugs,
  9. visual acuity, musculoskelatal abnormalities/chronic medical debilities,
  10. functional motor ability, and
  11. hearing

Utah CODES was funded to evaluate the effect of the existing medical condition licensing program on public safety. The project was funded in part by NHTSA, with the support of the Utah Driver License Division in the Utah Department of Public Safety, and the Utah Department of Transportation.

In order to determine the effects of this public safety program, we compared the citation, crash and at-fault crash rates of drivers licensed with medical conditions to those of similar drivers matched on age group, gender and county of residence. Comparison drivers were obtained randomly from the general driving population and rates of adverse driving events were examined over a five year period, 1992-1996. A two-to-one matching strategy was used. Sampling was performed with replacement.

Analyses were conducted for each functional ability or medical condition category by restriction status. Analyses for drivers licensed with multiple medical conditions were conducted separately, by restriction status. The previous analyses were also conducted separately for drivers who maintained one restriction status during the study period, and drivers whose restriction status fluctuated during the study period. We used probabilistic linkage to link data elements relating to the same driver from several different databases in order to combine the elements needed for the study (i.e., crash, violation and driver license databases).

The rates of citation, crash and at-fault crash varied between the populations and events of interest. Overall, unrestricted drivers licensed with single medical conditions had higher rates of citation, crash and at-fault crashes than the chosen comparison drivers. The differences were statistically significant, but of small magnitude. Restricted drivers licensed with single medical conditions during the study period had higher rates of crash and at-fault crash than unrestricted program drivers, but similar rates of citation. Analysis by individual functional ability categories (medical conditions), showed great variation. Of interest, the citation risk for unrestricted drivers licensed in the categories "cardiovascular" and "pulmonary" had significantly lower rates of citation than their chosen comparison drivers, but similar rates of crash and at-fault crash. The greatest citation risks were found in the restricted categories "learning, memory and communication disorders" and "alcohol and other drugs" where the rates were 11.63 and 5.83 times higher respectively than of the selected comparison drivers. However, these populations were extremely small (N=6 and N=24 respectively) so their impact on public safety was negligible. Similarly, the greatest risks for all crash and at-fault crash occurred in small, restricted driving populations licensed in the "musculoskelatal abnormalities" and "alcohol and other drugs" categories (N=32 and N=24 respectively).

Drivers who were licensed with more than one medical condition during the study period were analyzed separately. The risks for crash and at-fault crash were higher than those of the chosen comparison drivers for both restricted and unrestricted drivers. The magnitude of risk was highest for at-fault crash for drivers who had restrictions imposed on their driver licenses; the rate was 1.76 times higher than those of the chosen comparison drivers (95% CI 1.40, 2.28). The rates of citation for unrestricted drivers were similar and citation rates for restricted drivers were significantly lower than those of their respective comparison groups.

The results of this study provide contextual information on the effects of the medical conditions licensing program on public safety. Specifically, we found that the overall rates of adverse driving events varied between medical condition or category type, and restriction status. Of interest, in the largest functional ability category, cardiovascular (N=18,990), the rates for all adverse events were similar to those of their comparison groups for both restricted and unrestricted drivers; however, unrestricted drivers in this category had a slight but significantly lower rate of citation. For unrestricted drivers, the highest risk of at-fault crash was found in the learning, memory and communications category where the risk of at-fault crash was 3.63 times higher than their respective comparison group (95% CI 2.00, 6.60). The greatest differences in at-fault crash rates were found in restricted license categories. Restricted drivers in the musculoskelatal abnormality or chronic medical disability group had a rate 11.29 times higher than their comparison drivers (95% CI 2.39, 53.25).

As with any injury control intervention, evaluation is an essential component of the program in order to identify areas of increased risk and to provide feedback to the administering agency. Further research should be performed to evaluate the rates of adverse driving events by individual functional ability levels in order to determine if there are distinct levels for which risk increases or decreases, and to describe the effects of co-existing medical conditions for large categories. This information will help to identify areas where the program could be improved, as well as, help to identify functional ability categories where unnecessary restrictions could be eliminated.













Introduction

State of Utah Functional Ability in Driving: Guidelines and Standards for Health Care Professionals

The Utah Driver License Division implemented a program in 1979 to license drivers with medical conditions. In 1981, the Utah Driver License Division Medical Advisory Board redesigned the written standards of the program that describe the physical, mental and emotional capabilities appropriate for various types of driving. The intent of the board was to create the least restrictive program possible that was consistent with public safety.

The program uses a general questionnaire to screen all license applicants within the state to identify medical conditions related to the applicant's physical, mental and emotional health. Applicants who report a medical condition when completing the questionnaire are placed into at least one of twelve broad functional ability categories by medical history. The categories include:

  1. diabetes mellitus and other metabolic conditions,
  2. cardiovascular,
  3. pulmonary,
  4. neurologic,
  5. epilepsy and other episodic conditions,
  6. learning/memory/communications,
  7. psychiatric or emotional conditions,
  8. alcohol and other drugs,
  9. visual acuity,
  10. musculoskelatal abnormalities/chronic medical debilities,
  11. functional motor ability, and
  12. hearing.

Applicants who identify themselves as having a medical condition are further then classified by functional ability level. The ability level characterizes the driver's physical, mental or emotional condition according to the Utah program's guidelines. Scaling is done by a medical professional according to detailed guidelines provided by the program (Appendix B). The functional ability level corresponds to driver license privileges and license limitations as shown in Table 1. Drivers who place in functional ability levels 3 5 are unrestricted and have full license privileges while drivers at functional ability levels 6 11 are restricted with limitations on their licenses (e.g., speed, area and/or time of day limitations). Drivers at level 1 and 2 were not included. Level 1 is used for commercial drivers, and level 2 indicates a history of medical condition with recovery and these drivers are not required to participate in the program.

Table 1. Relationship of Functional Ability Profiles to Driving Risk/Responsibility or Limitation

Functional Ability
Profile Level

Driving Risk/Responsibility, License Class or Limitations

1 through 5

Driving of commercial vehicles, depending on individual profile category. Driving of private vehicles.

6

Driving with speed limitations

7

Driving with speed and area limitations

8

Driving with speed, area and time of day limitations

9

Driving accompanied by licensed driver with limitations of speed and/or area and/or time of day limitations as recommended by health care professional

10

Special driving limitations recommended by health care professional not covered above

11

Under evaluation may or may not drive, according to circumstances as

Determined by director, with medical advice as appropriate

12

No driving

Based upon the results of the questionnaire, an applicant may have a driver license immediately issued, or the applicant may be required to complete a more extensive health history form An applicant identified as having a medical condition may be required to provide documentation by a health care provider to verify his or her functional ability level before a license will be issued. Depending upon the functional ability category (medical condition) and functional ability level (1 12), an applicant who has a medical condition may receive full-unrestricted or restricted driving privileges, or the license application may be denied. Applicants who disagree with the level assigned by their health care provider may contest the level and have it reviewed by the Utah Driver License Medical Advisory Board. A copy of the State of Utah Functional Ability in Driving: Guidelines and Standards for Health Care Professionals is located in Appendix A. Copies of the general screening questionnaire, and the corresponding forms that are completed by health care professionals are located in Appendix B.

The Utah Crash Outcome Data Evaluation System

The Utah Crash Outcome Data Evaluation System (CODES) was created in 1992 at the University of Utah School of Medicine through a successful competitive funding application from the National Highway Traffic Safety Administration (NHTSA). Utah was one of the initial seven CODES states that used probabilistic linking techniques to link computerized data from motor vehicle crashes with those from several health care related data sets including emergency medical services and hospital inpatient and emergency department databases. The initial objective of CODES was to measure the effectiveness of safety belts and motorcycle helmets . Since its creation, Utah CODES has linked and analyzed state crash, ambulance, hospital inpatient and outpatient data in part or entirely for the years 1991 - 1997.

Utah CODES has become an integral partner with the Utah Department of Public Safety, the Utah Department of Health and the Utah Department of Transportation in injury control efforts related to traffic safety in the state. Analysis of the linked data sets has identified the medical and resulting financial outcomes for injuries caused by crashes. Utah specific data have been used to analyze the effects of pending legislative issues and to support changes that would be of benefit to public health and safety (e.g., implementation of a primary seatbelt law and graduated licensing program for teens). Because program staff have the capability and experience in probabilistic linkage and analytical techniques, Utah CODES was in a unique position to be able to perform the necessary linkages in order to evaluate the existing program of licensing drivers with medical conditions.

Evaluating the Existing Program of Licensing Drivers with Medical Conditions in Utah

Several agencies had approached Utah CODES about evaluating the medical conditions licensing program in the state. According to the Department of Public Safety, the licensing program is controversial; many drivers feel the program is unwarranted while others feel the standards set forth compromise public safety. Both the Utah Medical Advisory Board and the Utah Driver License Division were interested in evaluating the effects of the program. Additionally, NHTSA is in the process of developing a Functional Ability Driving Guide for state driver licensing agencies use to help design programs for drivers with functional disabilities. Research in this area is sparse; thus, the successes or failures of existing state programs related to functional ability are of particular interest. According to NHTSA, Utah's program and the corresponding guidelines have been considered by many states to be one of the most comprehensive functional ability and driving programs in the nation [2]. Because of these agencies and the applicability of the research to public policy, Utah CODES was funded to evaluate the effect of the existing system. The project was funded in part by NHTSA with the support of the Utah Driver License Division in the Utah Department of Public Safety and the Utah Department of Transportation.










OBJECTIVES

The purpose of the study was to compare the crash and citation rates of drivers with medical conditions to drivers without medical conditions, matched on age group, gender and county of residence, obtained from the general driving population. Analyses were performed for each functional ability (medical condition) category by restriction status for the study period 1992 1996. Analyses for drivers licensed with multiple medical conditions were performed separately, by restriction status. Additionally, the same analyses were performed separately for drivers who maintained one restriction status during the study period, and drivers whose restriction status fluctuated during the study period.








METHODOLOGY

Probabilistic Linkage

Probabilistic linkage was used to link data elements from several different databases in order to combine the elements needed for such a study . Probabilistic linkage is an iterative tool which can overcome inaccuracies or differences in the separate databases, (e.g., incorrect, missing or duplicate data, typographical errors, changes in surnames, etc.) which exact matching cannot. Data linkages were performed using Automatch SoftwareÒ and are described below:

Crash to Utah Master Driver License File

Variables from the Utah Department of Transportation Crash Files were linked to variables from the Utah Master Driver License File for the years 1992-1996. Fields used to link these two files included the license state of the crash driver, name (last, first, middle initial), sex, date of birth, and driver license number. The medical condition database was provided in a relational file to the Utah Master Driver License File.

The crash file identified 397,849 Utah licensed drivers as having a crash during the study period. The Utah Master Driver License File contained 1,750,918 drivers license records. Of the Utah licensed drivers in crashes, 384,311 (97%) drivers were successfully matched to the corresponding driver license records. A copy of the match file is located in Appendix C.

Utah Death Certificate Database to Utah Master Driver License File

Probabilistic linkage was used to identify persons who held valid driver licenses and died either during the study period, or in the five years previous to the study period. This linkage was performed because drivers licensed with medical conditions were thought to have a higher mortality rate than the general population of drivers and deaths would effect the eligible number of driving days. Variables used to link these two files included name (last, first, middle), city, state, residential zip code, sex, date of birth, and social security number.

The death certificate database was subset to include persons ages sixteen years and over (i.e., persons eligible for a driver license). Thus, the resulting data set contained 100,248 death certificates for the years 1986-96 that were linked to 1,750,918 drivers license records from the 1997 Utah Driver License Master File. Of these, 59,709 (59.6%) were successfully matched.

This matching procedure allowed a date of death variable to be created for drivers who died during the study period. By creating this variable, drivers who held valid driver licenses when they died could be excluded at the date of death (i.e., deceased persons cannot drive even though their license is still valid) and allowed the replacement of comparison drivers who died prior to the study start date. This procedure was performed in order to minimize misclassification bias of the number of days a driver was eligible to drive in the study. A copy of the match file is located in Appendix C.

Comparison Driver Selection

For an ideal comparison, crash and citation rates should be related to exposure, expressed as events per mile driven and controlled for risk factors that affect the likelihood of the event occurring. For example, if two drivers have the same number of crashes per year but one drives only half as much as the other, the rates are the same per unit time but two-fold higher when comparing driving distances. Additionally, factors such as weather, road surface, traffic conditions and speed limit may affect crash risk. Likewise, local law enforcement patterns in areas where drivers frequently drive affect the risk of citation.

This concept of measure of exposure is important when comparing the crash and citation rates of different populations, particularly in the older persons or persons who have medical conditions that may affect driving. During the study period, drivers who reported medical conditions in Utah were much different than the general population. Figure 1 illustrates the differences in ages between the medical condition drivers by restriction status and the rest of the driving population. Note that the general driving population is much younger overall than the medical conditions driving populations. Additionally, restricted drivers tend to be older than unrestricted drivers licensed with medical conditions. For this study, only drivers without medical conditions were eligible to be chosen as a comparison driver. This category excludes all drivers with medical conditions and drivers with incomplete information in the master driver license file.

Many studies have shown that drivers who do not feel that they can safely drive limit the amount they drive, or limit their driving to times or conditions when they feel comfortable to drive . For example, persons who do not see well at night may schedule trips during daylight hours.

While ideally a study to evaluate the medical conditions program would consider these factors, such data would have to be collected by a survey tailored to each functional ability category by restriction status. Because collecting these data would have been cost prohibitive, we determined that the best method to approximate these factors would be to match drivers with medical conditions to a comparison group. For each driver with a medical condition, two driving records of drivers without medical conditions from the same age group, gender and county of residence were selected for comparison.

Drivers in the medical conditions program were subdivided by functional ability category. The category "hearing" was excluded from analysis since this category was only used for commercial drivers. Drivers in each functional ability category were further subset by restriction status. If a driver with a medical condition fluctuated between restricted and unrestricted categories, he or she was counted in each category for the appropriate time period. The same comparison drivers were used for each medical condition driver who fluctuated for both restriction statuses. Comparison drivers were followed for the duration if they held a valid driver license during the study period. Drivers listed in multiple functional ability categories were analyzed by restriction status separately. These groupings were further separated into categories by age group, county of residence and gender. Age groups included years 10-14, 15-19, 20-24, 25-29, 30-39, 40-49, 50-59, 60-69, 70-79, 80 and older. Driver's age was calculated at the midpoint of the study period using the date of birth available in the Master Driver License File. We included the age group 10-14 in order to capture new drivers entering the study near the endpoint (1995-1996).

Comparison drivers were selected randomly from all licensed drivers not in a functional ability category from the 1997 master file. Commercial drivers who were licensed at functional ability level 1 (no history of disease/condition) were not included in the population from which a comparison driver could be selected. Similarly, drivers licensed at functional ability 2 (past history of disease/condition but licenses are issued the same as the general driving population) were excluded. For each driver with a medical condition, two comparison drivers fitting the grouping criteria (age group, county of residence and gender) were chosen at random from the Utah Master Driver License File. Sampling for comparison drivers was performed with replacement, meaning that each possible comparison driver was eligible to be selected even if that driver was chosen previously to be a comparison. This method was used because there were not enough drivers in some groupings to select two unique comparison drivers for each medical condition driver from the same age group, sex and county of residence.

The results of probabilistic linkage were used to determine the number of eligible licensed driving days by restriction status; and the number of crashes, at-fault crashes and citations occurring at that restriction status for each driver. Drivers with medical conditions who fluctuated between restriction status had the corresponding number of days at each status level assigned. As mentioned previously, drivers who died during the study period had their corresponding number of eligible driving days adjusted so that the date of death was included but the following days excluded. Similarly, if a chosen driver had his or her driving privileges suspended because of citations or crashes, they were not excluded from the study; the number of eligible license days was adjusted to reflect the suspension.

Comparison drivers were followed for the duration of the study (1992 1996) by their eligible number of driving days (the number of days they held a valid driver license) during the study period. The number of days used for these groups was higher than the number of days for drivers with medical conditions because the licensing periods are much shorter for drivers who have medical conditions. For example, if a driver with a medical condition was in the database for 1 year of the study period, he or she would be counted for 365 days. However, his or her corresponding driver would have been followed from 1992 1996, or 1,825 days. This was done in order to simplify the matching process and minimize the computer time used to generate the comparison drivers. The eligible number of driving days for both drivers with medical conditions and their comparisons reflects the data of the Utah Driver License Division. The same two comparison drivers were used for drivers whose medical condition fluctuated their restriction statuses. Events and eligible license days for these comparison drivers were counted at each restriction status.

Crashes were considered to be "at fault" if a driver received a citation for the crash or was marked as having contributed to the crash. Only crashes and citations that occurred during the period of time the driver was licensed were considered. Events (citation or crash) were corresponded to the driver's record, and restriction status. Citation, crash and at fault crash rates per eligible licensed driving day were calculated separately for restricted and unrestricted drivers with medical conditions and their corresponding drivers for each functional ability category. These data were then used to estimate the relative risk for each medical condition category, allowing a comparison of the crash or citation risk of drivers licensed with medical conditions to similar drivers licensed without medical conditions from the general driving population. The relative risk approximates a Chi Square distribution with one degree of freedom. Using this distribution we calculated a 95% confidence interval for the estimate of relative risk . Relative risk describes the influence of a particular variable on the likelihood of an outcome. For instance, unrestricted drivers in the visual acuity group have a relative risk for crashes of 1.35; this means that they were 1.35 times as likely to be in a crash as were members of the control group.











RESULTS

During 19921996, there were a total of 68,770 drivers in the medical conditions program excluding all commercial drivers and drivers in functional ability level two. The majority of drivers (54,825, 79.7%) were licensed in only one functional ability or medical condition category. A small number of these drivers had relatively unstable medical conditions (2,099, 3.8%) causing them to fluctuate between unrestricted, restricted or ineligible licensing functional ability levels during the study period. Table 2 shows the actual number of drivers reporting a single medical condition by functional ability category, and the corresponding numbers and percentages of drivers who fluctuated between restricted, unrestricted or ineligible license privileges during the study period.

Table 2. Drivers Reporting A Single Medical Condition by Functional Ability Category and Fluctuation Status, Utah Driver License Division, 1992 1995

Functional Ability Category

Total Number of Drivers Reporting Single Functional Ability Categories

Number of Drivers Fluctuating Between At Least Two of the Following Categories:

  1. Restricted License Privileges
  2. Unrestricted Licensing Privileges , or
  3. Ineligible for License

Percent

of Total

Diabetes & Other Metabolic Conditions

10,101

339

3.4%

Cardiovascular

19,031

125

0.7%

Pulmonary

2,684

178

6.6%

Neurologic

971

119

12.3%

Epilepsy and Other Episodic Conditions

2,709

745

27.5%

Learning, Memory and Communication

111

6

5.4%

Psychiatric or Emotional Conditions

6,805

282

4.1%

Alcohol and Other Drugs

148

19

12.8%

Visual Acuity

11,658

263

2.3%

Musculoskeletal Abnormality or Chronic Medical Debility

385

17

4.4%

Functional Motor Impairment

222

6

2.7%

Total

54,825

2,099

3.8%

The age group and sex distributions for each functional ability category, and each restriction status (unrestricted and restricted) are very different. Generally, restricted drivers tend to be older than unrestricted drivers. Population demographics shown by age group and sex histograms are presented in Appendix D.

The remaining drivers (13,832, 20.1%) were licensed in one or more functional ability categories during the study period. Most of the drivers reporting multiple conditions were licensed in two functional ability categories; however, the number per licensed driver ranged from one to seven categories during the study period . This is shown in Table 3.

Table 3. Number of Functional Ability Categories Reported by Drivers with Medical Conditions in Utah, 1992 1995

Number of Categories

Count

Percent

1

54,938

79.9%

2

10,595

15.4%

3

2,403

3.5%

4

653

0.9%

5

146

0.2%

6

28

0.0%

7

7

0.0%

Total

68,770

100.0%

 

Table 4 shows the two way categorical combinations for drivers who were licensed in multiple functional ability categories. Note that drivers may appear more than one time, depending upon the number of functional ability categories reported. The most common two way combinations of functional ability categories were "cardiovascular and diabetes," "cardiovascular and vision," and "cardiovascular and pulmonary."


Table 4. Two Way Combinations of Drivers Licensed in Multiple Functional Ability Categories, Utah Driver License Division, 1992- 1995

 

Diabetes

Cardio

Pulm

Neuro

Epilepsy

Learn

Psych

Alcohol

Vision

Musculo

 

 

 

 

 

 

 

 

 

 

 

 

 

Cardiovascular

5,436

 

 

 

 

 

 

 

 

 

 

Pulmonary

717

1,796

 

 

 

 

 

 

 

 

 

Neurologic

614

941

223

 

 

 

 

 

 

 

 

Epilepsy

173

280

89

369

 

 

 

 

 

 

 

Learning

102

197

48

380

117

 

 

 

 

 

 

Psychiatric

497

853

299

243

168

228

 

 

 

 

 

Alcohol

81

98

57

61

52

38

269

 

 

 

 

Vision

1,359

1,933

372

315

100

92

176

25

 

 

 

Musculoskelatal

401

574

205

547

80

127

194

53

180

 

 

Functional Motor

241

330

94

637

72

150

118

38

140

780

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2 shows the shows the percentages of drivers who were licensed in multiple functional ability categories, by each functional ability category. Over half of these drivers with multiple conditions were in the respective "cardiovascular" and "diabetes and other metabolic conditions" functional ability categories.

 



Analyses were performed for drivers who reported single medical conditions in the following ways: 1) combining all drivers licensed in one functional ability category who had either a constant restriction status (restricted or unrestricted) or whose status fluctuated during the study period, 2) for drivers who had a constant restriction status during the study period, and 3) for drivers who had a fluctuating restriction status during the study period. Drivers licensed in multiple functional ability categories during the study period were analyzed separately in the same manner.

The overall results for single medical condition drivers by combining restriction statuses for citations, crashes and at-fault crashes are presented in Tables 5 - 7. These tables show the estimates of risk for the event as compared to the risk for the event in the comparison drivers. Table 8 shows the estimates of risk for drivers licensed with multiple medical conditions, restriction statuses combined as compared to comparison drivers for the events of citation, all crash and at-fault crash. Similarly, the table shows the same comparisons for all single functional ability categories combined.

Tables 9 - 14 show in detail the rates and the estimate of risk for single medical condition drivers with combined restriction statuses for citation, crash and at-fault crash. These tables show the details of the information presented in the summary (Tables 5 - 7). Stratified analyses for the single condition drivers who had a constant restriction status for the study period and then those drivers who changed statuses during the study period for citation, crash, and at fault crash are shown in Tables 15 - 20. This analysis was performed to determine whether or not drivers with unstable conditions affected the combined analysis disproportionately. In these tables, drivers whose status changed are listed only once in each restriction status, regardless of the number of times their status fluctuated during the study period.

Table 5. Relative Risk for Driving Citations,

Functional Ability Category to Comparison Group, Single Medical Conditions Combined Restriction Status,

Utah 1992 1996

Functional Ability Category

Restriction Status

Relative Risk

95% Confidence Interval

Diabetes & Other Metabolic Conditions

Not Restricted

1.02

0.98, 1.07

 

Restricted

1.39

0.92, 2.09

Cardiovascular

Not Restricted

0.76 **

0.72, 0.88

 

Restricted

1.58

0.74, 3.38

Pulmonary

Not Restricted

0.87 **

0.79, 0.97

 

Restricted

0.49

0.18, 1.30

Neurologic

Not Restricted

0.92

0.76, 1.10

 

Restricted

0.76

0.44, 1.29

Epilepsy and Other Episodic Conditions

Not Restricted

1.02

0.96, 1.10

 

Restricted

1.05

0.81, 1.36

Learning, Memory and Communication

Not Restricted

1.26

0.85, 1.86

 

*Restricted

11.63 *

3.58, 37.78

Psychiatric or Emotional Conditions

Not Restricted

1.23 *

1.17, 1.30

 

Restricted

0.84

0.53, 1.33

Alcohol and Other Drugs

Not Restricted

2.38 *

1.82, 3.12

 

Restricted

5.83 *

3.19, 10.66

Visual Acuity

Not Restricted

1.35 *

1.27, 1.43

 

Restricted

1.31 *

1.10, 1.56

Musculoskeletal Abnormality or Chronic Medical Debility

Not Restricted

1.22

0.90, 1.65

 

Restricted

zero rate

 

Functional Motor Impairment

Not Restricted

1.42 *

1.04, 1.94

 

Restricted

zero rate

 

*The confidence interval does not include 1.0. Therefore, the higher rate of the medical conditions group is statistically significant. ** indicates that the medical conditions group has a statistically significant lower rate.






Table 6. Relative Risk for All Crashes,
Functional Ability Category to Comparison Group, Single Medical Conditions Combined Restriction Status,

Utah 1992 1996

Functional Ability Category

Restriction Status

Relative Risk

95% Confidence Interval

Diabetes & Other Metabolic Conditions

Not Restricted

1.30 *

1.23, 1.38

 

 

 

Restricted

1.38

0.75, 2.54

 

 

Cardiovascular

Not Restricted

0.99

0.93, 1.06

 

 

 

Restricted

1.37

0.43, 4.38

 

 

Pulmonary

Not Restricted

1.18 *

1.03. 1.34

 

 

 

Restricted

0.91

0.40, 2.09

 

 

Neurologic

Not Restricted

1.62 *

1.32, 1.99

 

 

 

Restricted

1.33

0.78, 2.28

 

 

Epilepsy and Other Episodic Conditions

Not Restricted

1.73 *

1.58, 1.90

 

 

 

Restricted

1.47 *

1.06, 2.03

 

 

Learning, Memory and Communication

Not Restricted

2.19 *

1.33, 3.61

 

 

 

Restricted

zero rate

 

 

 

Psychiatric or Emotional Conditions

Not Restricted

1.57 *

1.46, 1.67

 

 

 

Restricted

1.87 *

1.11, 3.17

 

 

Alcohol and Other Drugs

Not Restricted

1.82 *

1.18, 2.81

 

 

 

Restricted

4.21 *

1.80, 9.85

 

 

Visual Acuity

Not Restricted

1.35 *

1.25, 1.46

 

 

 

Restricted

1.27 *

1.04, 1.55

 

 

Musculoskeletal Abnormality or Chronic Medical Debility

Not Restricted

1.59 *

1.10, 2.29

 

 

 

Restricted

4.51 *

1.01, 20.12

 

 

Functional Motor Impairment

Not Restricted

1.11

0.70, 1.74

 

 

 

Restricted

zero rate

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 




Table 7. Relative Risk for At Fault Crashes,
Functional Ability Category to Comparison Group, Single Medical Conditions Combined Restriction Status,

Utah 1992 1996

Functional Ability Category

Restriction Status

Relative Risk

95% Confidence Interval

Diabetes & Other Metabolic Conditions

Not Restricted

1.46*

1.36, 1.58

 

Restricted

1.77

0.87, 3.61

Cardiovascular

Not Restricted

1.00

0.92, 1.09

 

Restricted

1.54

0.37, 6.40

Pulmonary

Not Restricted

1.26*

1.06, 1.50

 

Restricted

1.60

0.69, 3.71

Neurologic

Not Restricted

2.20*

1.71, 2.84

 

Restricted

1.40

0.71, 2.76

Epilepsy and Other Episodic Conditions

Not Restricted

2.02*

1.80, 2.27

 

Restricted

2.39*

1.70, 3.36

Learning, Memory and Communication

Not Restricted

3.32*

1.84, 5.59

 

Restricted

zero rate

 

Psychiatric or Emotional Conditions

Not Restricted

1.85*

1.69, 2.01

 

Restricted

2.89*

1.64, 5.07

Alcohol and Other Drugs

Not Restricted

2.22*

1.25, 3.94

 

Restricted

5.75*

2.26, 14.61

Visual Acuity

Not Restricted

1.52*

1.38, 1.68

 

Restricted

1.56*

1.25, 1.94

Musculoskeletal Abnormality or Chronic Medical Debility

Not Restricted

1.84*

1.14, 2.98

 

Restricted

11.29*

2.39, 53.25

Functional Motor Impairment

Not Restricted

1.71*

1.00, 2.93

 

Restricted

zero rate

 

*The confidence interval does not include 1.0. Therefore, the higher rate of the medical conditions group is statistically significant. ** indicates that the medical conditions group has a statistically significant lower rate.






Table 8. Adverse Driving Events for Drivers in Multiple Functional Ability Categories and Total Single Functional Ability Categories Compared to Comparison Groups for Combined Restriction Status, Utah 1992 - 1996

Adverse Driving Event

Restriction

Status

Relative

Risk

95% Confidence

Interval

Citations (Multiple)

Not Restricted

0.98

0.93, 1.03

 

Restricted

0.80**

0.65, 0.98

 

 

 

 

Crashes (Multiple)

Not Restricted

1.41*

1.33, 1.48

 

Restricted

1.28*

1.04, 1.58

 

 

 

 

At-Fault Crashes

Not Restricted

1.60*

1.49, 1.71

(Multiple)

Restricted

1.67*

1.31, 2.13

 

 

 

 

Citations

Not Restricted

1.09*

1.07, 1.12

(Combined Single)

Restricted

0.95

0.84, 1.07

 

 

 

 

Crashes

Not Restricted

1.33*

1.30, 1.33

(Combined Single)

Restricted

1.26*

1.08, 1.44

 

 

 

 

At-Fault Crashes

Not Restricted

1.49*

1.44, 1.55

(Combined Single)

Restricted

1.74

1.49, 2.04





Table 9. Relative Risk for Citations, Single Functional Ability Category and Corresponding Comparison Groups by Combined Restriction Status, Utah 1992 1996

Functional Ability Category

Restriction Status

Drivers

Medical Conditions

Comparison Group

Relative Risk

 

 

 

# Citations

# Days

Rate/10,000 days

Comparison

# Citations

# Days

Rate/10,000 days

 

Diabetes & Other Metabolic Conditions

Not Restricted

10,069

2,600

9,951,193

2.61

19,661

7,864

30,835,268

2.55

1.02

 

Restricted

358

24

54,199

4.43

716

337

1,054,327

3.20

1.39

Cardiovascular

Not Restricted

18,990

1,428

11,619,207

1.23

34,760

9,661

59,460,806

1.62

0.76 **

 

Restricted

160

7

22,290

3.14

320

99

499,038

1.98

1.58

Pulmonary

Not Restricted

2,615

438

1,953,578

2.24

5,200

2,009

7,839,653

2.56

0.87 **

 

Restricted

244

4

57,764

0.69

488

107

754,771

1.42

0.49

Neurologic

Not Restricted

887

138

653,869

2.11

1,773

626

2,715,370

2.31

0.92

 

Restricted

194

15

91,682

1.64

388

127

588,626

2.16

0.76

Epilepsy and Other Episodic Conditions

Not Restricted

2,620

1,068

2,627,369

4.06

5,227

3,064

7,719,599

3.97

1.02

 

Restricted

775

62

149,980

4.13

1,548

872

2,221,883

3.92

1.05

Learning, Memory and Communication

Not Restricted

107

32

66,465

4.81

214

114

298,154

3.82

1.26

 

Restricted

6

4

1,945

20.57

12

3

16,963

1.77

11.63 *

Psychiatric or Emotional Conditions

Not Restricted

6,763

2,081

5,287,313

3.94

13,402

6,512

20,397,764

3.19

1.23 *

 

Restricted

305

19

58,447

3.25

610

361

934,199

3.86

0.84

Alcohol and Other Drugs

Not Restricted

143

74

87,464

8.46

286

155

436,569

3.55

2.38 *

 

Restricted

24

12

6,004

19.99

48

26

75,893

3.43

5.83 *

Visual Acuity

Not Restricted

10,363

1,269

4,292,568

2.96

19,778

6,612

30,215,840

2.19

1.35 *

 

Restricted

1,535

157

872,499

1.80

2,987

604

4,390,829

1.38

1.31 *

Musculoskeletal Abnormality or Chronic Medical Debility

Not Restricted

370

53

224,975

2.36

739

222

1,149,840

1.93

1.22

 

Restricted

32

0

9,014

0.00

64

22

101,731

2.16

zero rate

Functional Motor Impairment

Not Restricted

214

51

147,593

3.46

428

161

659,761

2.44

1.42 *

 

Restricted

13

0

5,369

0.00

24

12

41,386

2.90

zero rate

*The confidence interval does not include 1.0. Therefore, the higher rate of the medical conditions group is statistically significant.

** indicates that the medical conditions group has a statistically significant lower rate.





Table 10. Confidence Interval for Relative Risk of Citations, Single Functional Ability Category and Corresponding Comparison Groups by Combined Restriction Status, Utah 1992 1996

Functional Ability Category

Restriction Status

Rate Ratio

All Citations

All Days

Chi-Square

Std Error

Log(L)

Log(U)

 

Lower

Upper

Diabetes & Other Metabolic Conditions

Not Restricted

1.02

10,464

40,786,461

1.14

0.02

-0.02

0.07

0.98

1.07

 

Restricted

1.39

361

1,108,526

2.40

0.21

-0.09

0.74

0.92

2.09

Cardiovascular

Not Restricted

0.76

11,089

71,080,013

97.59

0.03

-0.33

-0.22

0.72

0.80

 

Restricted

1.58

106

521,328

1.40

0.39

-0.30

1.22

0.74

3.38

Pulmonary

Not Restricted

0.87

2,447

9,793,231

6.43

0.05

-0.24

-0.03

0.79

0.97

 

Restricted

0.49

111

812,535

2.07

0.50

-1.69

0.26

0.18

1.30

Neurologic

Not Restricted

0.92

764

3,369,239

0.88

0.09

-0.27

0.10

0.76

1.10

 

Restricted

0.76

142

680,308

1.03

0.27

-0.81

0.26

0.44

1.29

Epilepsy and Other Episodic Conditions

Not Restricted

1.02

4,132

10,346,968

0.45

0.04

-0.05

0.09

0.96

1.10

 

Restricted

1.05

934

2,371,863

0.16

0.13

-0.21

0.31

0.81

1.36

Learning, Memory and Communication

Not Restricted

1.26

146

364,619

1.33

0.20

-0.16

0.62

0.85

1.86

 

Restricted

11.63

7

18,908

16.65

0.60

1.28

3.63

3.58

37.78

Psychiatric or Emotional Conditions

Not Restricted

1.23

8,593

25,685,077

69.35

0.03

0.16

0.26

1.17

1.30

 

Restricted

0.84

380

992,646

0.54

0.24

-0.63

0.29

0.53

1.33

Alcohol and Other Drugs

Not Restricted

2.38

229

524,033

40.20

0.14

0.60

1.14

1.82

3.12

 

Restricted

5.83

38

81,897

32.89

0.31

1.16

2.37

3.19

10.66

Visual Acuity

Not Restricted

1.35

7,881

34,508,408

97.08

0.03

0.24

0.36

1.27

1.43

 

Restricted

1.31

761

5,263,328

9.04

0.09

0.09

0.44

1.10

1.56

Musculoskeletal Abnormality or Chronic Medical Debility

Not Restricted

1.22

275

1,374,815

1.70

0.15

-0.10

0.50

0.90

1.65

 

Restricted

zero rate

22

110,745

1.95

 

 

 

 

 

Functional Motor Impairment

Not Restricted

1.42

212

807,354

4.73

0.16

0.03

0.66

1.04

1.94

 

Restricted

zero rate

12

46,755

1.56

 

 

 

 

 

*The confidence interval does not include 1.0. Therefore, the higher rate of the medical conditions group is statistically significant.

** indicates that the medical conditions group has a statistically significant lower rate.





Table 11. Relative Risk for All Crashes, Single Functional Ability Category and Corresponding Comparison Groups by Combined Restriction Status, Utah 1992 1996

Functional Ability Category

Restriction Status

Drivers

Medical Conditions

Comparison Group

Relative

# Crashes

# Days

Rate/10,000 days

Comparison

# Crashes

# Days

Rate

Risk

Diabetes & Other Metabolic Conditions

Not Restricted

10,069

1,693

9,951,193

1.70

19,661

4,023

30,835,268

1.30

1.30*

 

Restricted

358

11

54,199

2.03

716

155

1,054,327

1.47

1.38

Cardiovascular

Not Restricted

18,990

1,209

11,619,207

1.04

34,760

6,233

59,460,806

1.05

0.99

 

Restricted

160

3

22,290

1.35

320

49

499,038

0.98

1.37

Pulmonary

Not Restricted

2,615

297

1,953,578

1.52

5,200

1,013

7,839,653

1.29

1.18*

 

Restricted

244

6

57,764

1.04

488

86

754,771

1.14

0.91

Neurologic

Not Restricted

887

124

653,869

1.90

1,773

318

2,715,370

1.17

1.62*

 

Restricted

194

16

91,682

1.75

388

77

588,626

1.31

1.33

Epilepsy and Other Episodic Conditions

Not Restricted

2,620

708

2,627,369

2.69

5,227

1,200

7,719,599

1.55

1.73*

 

Restricted

775

40

149,980

2.67

1,548

403

2,221,883

1.81

1.47*

Learning, Memory and Communication

Not Restricted

107

22

66,465

3.31

214

45

298,154

1.51

2.19*

 

Restricted

6

1

1,945

5.14

12

0

16,963

0.00

zero rate

Psychiatric or Emotional Conditions

Not Restricted

6,763

1,184

5,287,313

2.24

13,402

2,917

20,397,764

1.43

1.57*

 

Restricted

305

15

58,447

2.57

610

128

934,199

1.37

1.87*

Alcohol and Other Drugs

Not Restricted

143

27

87,464

3.09

286

74

436,569

1.70

1.82*

 

Restricted

24

6

6,004

9.99

48

18

75,893

2.37

4.21*

Visual Acuity

Not Restricted

10,363

753

4,292,568

1.75

19,778

3,931

30,215,840

1.30

1.35*

 

Restricted

1,535

122

872,499

1.40

2,987

484

4,390,829

1.10

1.27*

Musculoskeletal Abnormality or Chronic Medical Debility

Not Restricted

370

37

224,975

1.64

739

119

1,149,840

1.03

1.59*

 

Restricted

32

2

9,014

2.22

64

5

101,731

0.49

4.51*

Functional Motor Impairment

Not Restricted

214

23

147,593

1.56

428

93

659,761

1.41

1.11

 

Restricted

13

0

5,369

0.00

24

7

41,386

1.69

zero rate

*The confidence interval does not include 1.0. Therefore, the higher rate of the medical conditions group is statistically significant.

** indicates that the medical conditions group has a statistically significant lower rate.





Table 12. Confidence Interval for Relative Risk of All Crashes, Single Functional Ability Category and Corresponding Comparison Groups by Combined Restriction Status, Utah 1992 1996

Functional Ability Category

Restriction Status

Relative Risk

All Crashes

All Days

Chi-Square

Std Error

Log(L)

Log(U)

Lower

Upper

Diabetes & Other Metabolic Conditions

Not Restricted

1.30

5,716

40,786,461

84.45

0.03

0.21

0.32

1.23

1.38

 

 

Restricted

1.38

166

1,108,526

1.08

0.31

-0.29

0.93

0.75

2.54

 

Cardiovascular

Not Restricted

0.99

7,442

71,080,013

0.06

0.03

-0.07

0.05

0.93

1.06

 

 

Restricted

1.37

52

521,328

0.28

0.59

-0.85

1.48

0.43

4.38

 

Pulmonary

Not Restricted

1.18

1,310

9,793,231

6.08

0.07

0.03

0.29

1.03

1.34

 

 

Restricted

0.91

92

812,535

0.05

0.42

-0.92

0.73

0.40

2.09

 

Neurologic

Not Restricted

1.62

442

3,369,239

21.13

0.10

0.28

0.69

1.32

1.99

 

 

Restricted

1.33

93

680,308

1.11

0.27

-0.25

0.82

0.78

2.28

 

Epilepsy and Other Episodic Conditions

Not Restricted

1.73

1,908

10,346,968

138.20

0.05

0.46

0.64

1.58

1.90

 

 

Restricted

1.47

443

2,371,863

5.48

0.16

0.06

0.71

1.06

2.03

 

Learning, Memory and Communication

Not Restricted

2.19

67

364,619

9.59

0.26

0.29

1.28

1.33

3.61

 

 

Restricted

Zero Rate

1

18,908

8.72

 

 

 

 

 

 

Psychiatric or Emotional Conditions

Not Restricted

1.57

4,101

25,685,077

172.23

0.03

0.38

0.52

1.46

1.67

 

 

Restricted

1.87

143

992,646

5.46

0.27

0.10

1.15

1.11

3.17

 

Alcohol and Other Drugs

Not Restricted

1.82

101

524,033

7.32

0.22

0.17

1.03

1.18

2.81

 

 

Restricted

4.21

24

81,897

11.03

0.43

0.59

2.29

1.80

9.85

 

Visual Acuity

Not Restricted

1.35

4,684

34,508,408

56.88

0.04

0.22

0.38

1.25

1.46

 

 

Restricted

1.27

606

5,263,328

5.54

0.10

0.04

0.44

1.04

1.55

 

Musculoskeletal Abnormality or Chronic Medical Debility

Not Restricted

1.59

156

1,374,815

6.16

0.19

0.10

0.83

1.10

2.29

 

 

Restricted

4.51

7

110,745

3.91

0.76

0.01

3.00

1.01

20.12

 

Functional Motor Impairment

Not Restricted

1.11

116

807,354

0.19

0.23

-0.36

0.56

0.70

1.74

 

 

Restricted

Zero Rate

7

46,755

0.91

 

 

 

 

 

 

*The confidence interval does not include 1.0. Therefore, the higher rate of the medical conditions group is statistically significant.

** indicates that the medical conditions group has a statistically significant lower rate.






Table 13. Relative Risk for At Fault Crashes, Single Functional Ability Category and Corresponding Comparison Groups by Combined Restriction Status, Utah 1992 1996

Functional Ability Category

Restriction Status

Drivers

Medical Conditions

Comparison

Relative Risk

 

 

 

# Crashes

# Days

Rate/10,000 days

Comparison

# Crashes

# Days

Rate/10,000 days

Diabetes & Other Metabolic Conditions

Not Restricted

10,069

1,013

9,951,193

1.02

19,661

2,146

30,835,268

0.70

1.46*

 

Restricted

358

8

54,199

1.48

716

88

1,054,327

0.83

1.77

Cardiovascular

Not Restricted

18,990

637

11,619,207

0.55

34,760

3,256

59,460,806

0.55

1.00

 

Restricted

160

2

22,290

0.90

320

29

499,038

0.58

1.54

Pulmonary

Not Restricted

2,615

167

1,953,578

0.85

5,200

533

7,839,653

0.68

1.26*

 

Restricted

244

6

57,764

1.04

488

49

754,771

0.65

1.60

Neurologic

Not Restricted

887

86

653,869

1.32

1,773

162

2,715,370

0.60

2.20*

 

Restricted

194

10

91,682

1.09

388

46

588,626

0.78

1.40

Epilepsy and Other Episodic Conditions

Not Restricted

2,620

463

2,627,369

1.76

5,227

673

7,719,599

0.87

2.02*

 

Restricted

775

36

149,980

2.40

1,548

223

2,221,883

1.00

2.39*

Learning, Memory and Communication

Not Restricted

107

17

66,465

2.56

214

23

298,154

0.77

3.32*

 

Restricted

6

1

1,945

5.14

12

0

16,963

0.00

zero rate

Psychiatric or Emotional Conditions

Not Restricted

6,763

727

5,287,313

1.37

13,402

1,520

20,397,764

0.75

1.85*

 

Restricted

305

13

58,447

2.22

610

72

934,199

0.77

2.89*

Alcohol and Other Drugs

Not Restricted

143

16

87,464

1.83

286

36

436,569

0.82

2.22*

 

Restricted

24

5

6,004

8.33

48

11

75,893

1.45

5.75*

Visual Acuity

Not Restricted

10,363

493

4,292,568

1.15

19,778

2,280

30,215,840

0.75

1.52*

 

Restricted

1,535

102

872,499

1.17

2,987

329

4,390,829

0.75

1.56*

Musculoskeletal Abnormality or Chronic Medical Debility

Not Restricted

370

22

224,975

0.98

739

61

1,149,840

0.53

1.84*

 

Restricted

32

2

9,014

2.22

64

2

101,731

0.20

11.29*

Functional Motor Impairment

Not Restricted

214

18

147,593

1.22

428

47

659,761

0.71

1.71*

Restricted

13

0

5,369

0.00

24

5

41,386

1.21

zero rate

*The confidence interval does not include 1.0. Therefore, the higher rate of the medical conditions group is statistically significant.

** indicates that the medical conditions group has a statistically significant lower rate.






Table 14. Confidence Interval for Relative Risk of At Fault Crashes, Single Functional Ability Category and Corresponding Comparison Groups by Combined Restriction Status, Utah 1992 1996

Functional Ability Category

Restriction Status

Relative Risk

All Crashes

All Days

Chi-Square

Std Error

Log(L)

Log(U)

Lower

Upper

Diabetes & Other Metabolic Conditions

Not Restricted

1.46*

3,060

40,786,461

100.72

0.04

0.31

0.45

1.36

1.58

 

Restricted

1.77

95

1,108,526

2.45

0.36

-0.14

1.28

0.87

3.61

Cardiovascular

Not Restricted

1.00

3,712

71,080,013

0.00

0.04

-0.08

0.09

0.92

1.09

 

Restricted

1.54

28

521,328

0.36

0.73

-0.99

1.86

0.37

6.40

Pulmonary

Not Restricted

1.26*

668

9,793,231

6.70

0.09

0.06

0.40

1.06

1.50

 

Restricted

1.60

54

812,535

1.20

0.43

-0.37

1.31

0.69

3.71

Neurologic

Not Restricted

2.20*

243

3,369,239

36.97

0.13

0.54

1.05

1.71

2.84

 

Restricted

1.40

53

680,308

0.92

0.35

-0.35

1.01

0.71

2.76

Epilepsy and Other Episodic Conditions

Not Restricted

2.02*

1,105

10,346,968

141.55

0.06

0.59

0.82

1.80

2.27

 

Restricted

2.39*

249

2,371,863

25.10

0.17

0.53

1.21

1.70

3.36

Learning, Memory and Communication

Not Restricted

3.32*

38

364,619

15.81

0.30

0.61

1.79

1.84

5.99

 

Restricted

zero rate

1

18,908

8.72

 

 

 

 

 

Psychiatric or Emotional Conditions

Not Restricted

1.85*

2,159

25,685,077

190.39

0.04

0.53

0.70

1.69

2.01

 

Restricted

2.89*

82

992,646

13.57

0.29

0.50

1.62

1.64

5.07

Alcohol and Other Drugs

Not Restricted

2.22*

50

524,033

7.41

0.29

0.22

1.37

1.25

3.94

 

Restricted

5.75*

16

81,897

13.47

0.48

0.81

2.68

2.26

14.61

Visual Acuity

Not Restricted

1.52*

2,659

34,508,408

72.58

0.05

0.32

0.52

1.38

1.68

 

Restricted

1.56*

418

5,263,328

15.66

0.11

0.22

0.67

1.25

1.94

Musculoskeletal Abnormality or Chronic Medical Debility

Not Restricted

1.84*

80

1,374,815

6.24

0.24

0.13

1.09

1.14

2.98

 

Restricted

11.29*

4

110,745

9.37

0.79

0.87

3.97

2.39

53.25

Functional Motor Impairment

Not Restricted

1.71*

61

807,354

3.85

0.27

0.00

1.07

1.00

2.93

 

Restricted

zero rate

4

46,755

0.65

 

 

 

 

 

*The confidence interval does not include 1.0. Therefore, the higher rate of the medical conditions group is statistically significant.

** indicates that the medical conditions group has a statistically significant lower rate.

The results for drivers licensed with multiple medical conditions during the study period are presented in the following tables. Tables 15 - 16 contain the combined results of drivers with multiple and single restrictions status for citation, crash and at fault crash.






Table 15. Relative Risk for Adverse Driving Events, Drivers with Multiple Medical Conditions and Corresponding Comparison Groups by Combined Restriction Status, Utah 1992 1996

 

Restriction Status

Medical Conditions

Comparison Group

Rate Ratio

Drivers

# Events

# Days

Rate

Comparison

# Events

# Days

Rate

Ratio

L 95%

U 95%

Significance

Citation

Not Restricted

13,408

2,122

12,430,892

1.71

25,496

7,2247

41,429,463

1.74

0.98

0.93

1.03

 

 

Restricted

2,414

100

662,027

1.51

4,774

1,380

7,322,259

1.88

0.80

0.65

0.98

**

Crash

Not Restricted

13,408

1,965

12,430,892

1.58

25,496

4,659

41,429,463

1.12

1.41

1.33

1.45

*

 

Restricted

2,414

97

662,027

1.47

4,774

840

7,322,259

1.15

1.28

1.04

1.58

*

At Fault Crash

Not Restricted

13,408

1,229

12,430,892

0.99

25,496

2,567

41,429,463

.62

1.60

1.49

1.71

*

 

Restricted

2,414

73

662,027

1.10

4,774

483

7,322,259

.66

1.67

1.31

2.13

*

*The confidence interval does not include 1.0. Therefore, the higher rate of the medical conditions group is statistically significant.

** indicates that the medical conditions group has a statistically significant lower rate.






Table 16. Relative Risk for Adverse Driving Events, All Drivers with Single Functional Ability Category and Corresponding Comparison Groups by Combined Restriction Status, Utah 1992 1996

 

Restriction Status

Medical Conditions

Comparison Group

Rate Ratio

Drivers

# Events

# Days

Rate

Comparison

# Events

# Days

Rate

Ratio

L 95%

U 95%

Significance

Citation

Not Restricted

53,141

9,232

36,911,594

2.50

101,468

37,000

161,728,624

2.29

1.09

1.07

1.12

*

 

Restricted

3,646

304

1,329,193

2.29

7,205

2,570

10,679,646

2.41

0.95

0.84

1.07

 

Crash

Not Restricted

53,141

6,077

36,911,594

1.65

101,468

19,966

161,728,624

1.23

1.33

1.30

1.37

*

 

Restricted

3,646

222

1,329,193

1.67

7,205

1,412

10,679,646

1.32

1.26

1.08

1.44

*

At Fault Crash

Not Restricted

53,141

3,659

36,911,594

0.99

101,468

10,737

161,728,624

.66

1.49

1.44

1.55

*

 

Restricted

3,646

185

1,329,193

1.39

7,205

854

10,679,646

0.80

1.74

1.49

2.04

*

*The confidence interval does not include 1.0. Therefore, the higher rate of the medical conditions group is statistically significant.

** indicates that the medical conditions group has a statistically significant lower rate.




Diabetes mellitus and other metabolic conditions

This category included 10,069 licensed drivers with diabetes mellitus and thyroid, parathyroid, pituitary or other metabolic conditions. These results exclude the 7,245 drivers licensed in this category along with other medical conditions. Overall rates for unrestricted drivers in this category were 2.61, 1.70, and 1.02 per 10,000 license days for citation, all crash and at fault crashes respectively compared to 2.55, 1.30 and 0.70 respectively for their corresponding comparison group. Rates for restricted drivers in this category were 4.43, 2.03 and 1.48 per 10,000 licensed days compared to 3.20, 1.47 and 0.83 for their corresponding comparison group.

The relative risks for citation, crash and at fault crashes were 1.02, 1.30 and 1.46 for unrestricted drivers and 1.39, 1.38 and 1.77 for restricted drivers during the study period. The rates for all crashes and at-fault crashes in unrestricted drivers in this category were higher than those of the comparison group at a statistical significance level of 5%. Citations in unrestricted drivers, and all adverse driving events in the restricted drivers were not significantly different than the rates of the corresponding comparison groups.

Cardiovascular conditions

This category included 18,990 licensed drivers with cardiovascular conditions including heart disease, rhythm disturbances, or history of myocardial infarctions, heart surgery or hypertension. This excludes the 9,504 drivers who were licensed in the cardiovascular conditions category along with other functional ability categories. Rates for unrestricted drivers in this category were 1.23, 1.04, and 0.55 per 10,000 license days for citation, all crash and at fault crashes respectively compared to 1.62, 1.05 and 0.55 respectively for their corresponding comparison group. Rates for restricted drivers in this category were 3.14, 1.35 and 0.90 per 10,000 licensed days compared to 1.98, 0.98 and 0.58 for their corresponding comparison group.

The relative risks for citation, crash and at fault crashes were 0.76, 0.99 and 1.00 for unrestricted drivers and 1.58, 1.37 and 1.54 for restricted drivers during the study period. The rates for crash and at fault crashes for both restricted and unrestricted drivers in this category were not different than those of their comparison groups at a statistical significance level of 5%; however, unrestricted drivers had a statistically significant lower rate for citations.

Pulmonary conditions

This category includes 2,615 drivers licensed with pulmonary conditions including pulmonary disease or symptoms, impaired function or severe respiratory difficulties. This excludes the 2,552 drivers who were licensed in the pulmonary conditions category along with other functional ability categories. Rates for unrestricted drivers in this category were 2.24, 1.52, and 0.85 per 10,000 license days for citation, all crash and at fault crashes respectively compared to 2.56, 1.29 and 0.68 respectively for their corresponding comparison group. Rates for restricted drivers in this category were 0.69, 1.04 and 1.04 per 10,000 licensed days compared to 1.42, 1.14 and 0.65 for their corresponding comparison group.

The relative risks for citation, crash and at fault crashes were 0.87, 1.18 and 1.26 for unrestricted drivers and 0.49, 0.91 and 1.62 for restricted drivers during the study period. For unrestricted drivers, all of the differences between the pulmonary condition drivers and their corresponding comparison group were statistically significant. Unrestricted drivers with pulmonary conditions had a statistically significant lower rates for citation, and higher rates for all crash and at fault crash when compared to their comparison group at a significance level of 5%. The confidence intervals for restricted drivers for all three events included 1.0 meaning that there were no differences identified in the rates when compared to those of the corresponding comparison group.

Neurological conditions

This category includes 887 drivers with neurological conditions including strokes, head injuries, Cerebral Palsy, Multiple Sclerosis, Parkinson's disease, progressive conditions such as muscular atrophies and dystrophy, myasthenia gravis and other spinal cord and brain diseases. This excludes the 2,352 drivers who were licensed with neurological conditions along with other functional ability categories. Approximately 12.3% (119) of the drivers in this category fluctuated between unrestricted, restricted and ineligible driver license statuses. Epilepsy is considered a separate functional ability category. Rates for unrestricted drivers in this category were 2.11, 1.90 and 1.32 per 10,000 license days for citation, all crash and at fault crashes respectively compared to 2.31, 1.17 and 0.60 respectively for their corresponding comparison group. Rates for restricted drivers in this category were 1.64, 1.75 and 1.09 per 10,000 licensed days compared to 2.16, 1.31 and 0.78 for their corresponding comparison group.

The relative risks for citation, crash and at fault crashes were 0.92, 1.62 and 2.20 for unrestricted drivers, and 0.76, 1.33 and 1.46 for restricted drivers during the study period. The rates for crash and at-fault crashes were higher for unrestricted drivers at a statistical significance level of 5%, when compared to the rates of the comparison group. The confidence intervals for citations in the unrestricted drivers and all events for the restricted drivers included 1.0. This means that there was no difference in the rates of citation, crash, and at fault crash when compared to the rates of the comparison group.

Epilepsy and other episodic conditions

This category includes 2,620 drivers with epilepsy or other episodic conditions including syncope, cataplexy, narcolepsy, hypoglycemia, and episodic vertigo that interferes with function. This excludes the 934 drivers who were licensed with epilepsy along with other functional ability categories. Approximately 27.5% (745) of the drivers in this category fluctuated between unrestricted, restricted and ineligible driver license statuses. The rates for unrestricted drivers in this category were 4.06, 2.69 and 1.76 per 10,000 license days for citation, all crash and at fault crashes respectively compared to 3.97, 1.55 and 0.87 respectively for their corresponding comparison group. Rates for restricted drivers in this category were 4.13, 2.67 and 2.40 per 10,000 licensed days compared to 3.92, 1.81 and 1.00 for their corresponding comparison group.

The relative risks for citation, crash and at fault crashes were 1.02, 1.73 and 2.02 for unrestricted drivers and 1.05, 1.47 and 2.39 for restricted drivers during the study period. The relative risks for citation for unrestricted and restricted drivers included 1.0 meaning that the rates of citation were not different from those of the comparison groups at a statistical significance level of 5%. However, the rates for crash and at-fault crash for both groups were significantly higher than those of the comparison groups at a statistical significance level of 5%.

Learning, memory and communication

This category includes 107 drivers with history of impairment for learning, memory or communication and/or cognitive deficits. Persons with Alzheimer's disease are included in this category. This excludes the 732 drivers who were licensed with learning, memory or communication disorders along with other functional ability categories. Rates for unrestricted drivers in this category were 4.81, 3.31 and 2.56 per 10,000 license days for citation, all crash and at fault crashes respectively compared to 3.82, 1.51 and 0.77 respectively for their corresponding comparison group. Rates for restricted drivers in this category were 20.57, 5.14 and 5.14 per 10,000 licensed days compared to 1.77, 0 and 0 for their corresponding comparison group.

The relative risks for citation, crash and at fault crashes were 1.26, 2.19 and 3.32 for unrestricted drivers and 11.63 for citations for restricted drivers during the study period. Because the restricted comparison group did not have any crashes during the study period, statistical tests to evaluate the differences between the medical condition group and the comparison group could not be performed. Rates of crash and at-fault crash for unrestricted drivers, were higher than those of their corresponding comparison groups at a statistical significance level of 5%. Similarly, the rate of citation in restricted drivers was statistically higher than that of the comparison group at a significance level of 5%.

Psychiatric or emotional conditions

This category includes 6,703 drivers with history of psychiatric or emotional conditions, psychotic illness, including suicidal tendencies, perceptual distortions, psychomotor retardation, schizophrenia, major depressive disorders, bipolar disorders and/or organic brain syndromes. This does not include the 2,065 drivers who were licensed in this category along with other functional ability categories. Rates for unrestricted drivers in this category were 3.94, 2.24 and 1.37 per 10,000 license days for citation, all crash and at fault crashes respectively compared to 3.19, 1.43 and 0.75 respectively for their corresponding comparison group. Rates for restricted drivers in this category were 3.25, 2.57 and 2.22 per 10,000 licensed days compared to 3.86, 1.37, and 0.77 for their corresponding comparison group.

The relative risks for citation, crash and at fault crashes were 1.23, 1.57 and 1.85 for unrestricted drivers and 0.84, 1.81 and 2.89 for restricted drivers during the study period. The confidence levels for both restricted and unrestricted drivers for all events, except the citation risk for restricted drivers were higher when compared to those of the comparison groups at a statistical significance level of 5%.

Alcohol and other drugs

This category includes 143 drivers with history of drug including alcohol abuse. This does not include the 465 drivers who were licensed with alcohol and other drug conditions along with other functional ability categories. Approximately 12.8% (19) of the drivers in this category fluctuated between unrestricted, restricted and ineligible driver license statuses. Rates for unrestricted drivers in this category were 8.46, 3.09 and 1.83 per 10,000 license days for citation, all crash and at fault crashes respectively compared to 3.55, 1.70 and 0.82 respectively for their corresponding comparison group. Rates for restricted drivers in this category were 19.99, 9.99 and 8.33 per 10,000 licensed days compared to 3.43, 2.37 and 1.45 for their corresponding comparison group.

The relative risks for citation, crash and at fault crashes were 2.38, 1.82 and 2.22 for unrestricted drivers and 5.83, 4.21 and 5.75 for restricted drivers during the study period. The rates of all three adverse events were statistically higher in both restricted and unrestricted drivers. However, it is important to note that the number of restricted drivers in this category was extremely small (N=24), and while the differences were significant between these drivers and those chosen as comparisons, the confidence intervals for the risk ratio were large.

Visual acuity

This category includes 11,363 drivers with history of eye conditions that may affect vision function. Rates for unrestricted drivers in this category were 2.96, 1.75 and 1.15 per 10,000 license days for citation, all crash and at fault crashes respectively compared to 2.19, 1.30 and 0.75 respectively for their corresponding comparison group. Rates for restricted drivers in this category were 1.80, 1.40 and 1.17 per 10,000 licensed days compared to 1.38, 1.10 and 0.75 for their corresponding comparison group.

The relative risks for citation, crash and at fault crashes were 1.35, 1.35 and 1.52 for unrestricted drivers and 1.31, 1.42 and 1.56 for restricted drivers during the study period. The rates for citation, crash, and at fault crash were higher than the those of the comparison drivers for both groups at a statistical significance level of 5%.

Musculoskelatal abnormality or chronic medical debility

This category includes 370 drivers with history of a condition or disease that may affect driving safety (e.g., osteoporosis or active infectious disease, including HIV). This does not include the 1,603 drivers who were licensed in this category along with other functional ability categories. Rates for unrestricted drivers in this category were 2.36, 1.64 and 0.98 per 10,000 license days for citation, all crash and at fault crashes respectively compared to 1.93, 1.03 and 0.53 respectively for their corresponding comparison group. Rates for restricted drivers in this category were 0, 2.22 and 2.22 per 10,000 licensed days compared to 2.16, 0.49 and 0.20 for their corresponding comparison group.

The relative risks for citation, crash and at fault crashes were 1.22, 1.59 and 1.84 for unrestricted drivers and 0, 4.51 and 11.29 for restricted drivers during the study period. The rates for all crash and at-fault crash were higher for both restricted and unrestricted drivers than those of the corresponding comparison groups at a statistical significance level of 5%. The rates of citation for both restricted and unrestricted drivers were similar to those of the corresponding comparison groups. It is important to note that the number of restricted drivers in this category was small (N=32). Additionally, no citation events occurred during the study period for this group.

Functional motor impairment

This category includes 214 drivers with history of impaired functional motor ability including difficulties with muscular strength, coordination, range and motion, spinal movement and stability, amputations or the absence of body parts and/or abnormalities affecting motor comparison. This does not include the 1,280 drivers who were licensed in this category along with other functional ability categories. Rates for unrestricted drivers in this category were 3.46, 1.56 and 1.22 per 10,000 license days for citation, all crash and at fault crashes respectively compared to 2.44, 1.41 and 0.71 respectively for their corresponding comparison group. The rates for the restricted drivers in this category were 0, 0 and 0 per 10,000 licensed days compared to 2.90, 1.69 and 1.21 for their corresponding comparison group. Because the sample size for restricted drivers (N=13) was small, and no events occurred, statistical testing for restricted drivers could not be performed.

The relative risks for citation, crash and at fault crashes were 1.42, 1.18 and 1.87 for unrestricted drivers during the study period. The confidence levels for citation and at fault crash did not include 1.0. This means that the rates of citation and at fault crash were higher than those of the comparison group at a statistical significance level of 5%.

Drivers licensed in multiple functional ability categories

This category includes 13,408 drivers licensed during the study period. Rates for unrestricted drivers in this category were 1.71, 1.58 and 0.99 per 10,000 license days for citation, all crash and at fault crashes respectively compared to 1.74, 1.12 and 0.62 respectively for their corresponding comparison group. The rates for the restricted drivers in this category were 1.51, 1.47 and 1.10 per 10,000 licensed days for citation, crash and at fault crash compared to 1.88, 1.15 and 0.66 for their corresponding comparison group.

The relative risks for citation, crash and at fault crashes were 0.98, 1.41 and 1.60 for unrestricted drivers, and 0.80, 1.28 and 1.67 for restricted drivers for citation, crash and at fault crash during the study period. The confidence levels for all crash and at-fault crash in both groups were higher than those of their respective comparison groups at a statistical significance level of 5%. However, the rate of citation for restricted drivers was significantly lower than that of their corresponding comparison group, while the rate of citation for unrestricted drivers was similar to the rate of the comparison drivers.

Comparing drivers with a single restriction status to drivers whose restriction status fluctuated during the study period

In order to determine if there were differences in the rates between drivers whose condition remained stable for their duration of eligibility during the study period, and those whose condition was not stable, we stratified the previously presented analyses. The same analyses were performed separately for drivers who remained in one functional ability level (restricted or unrestricted) for the entire study, and drivers who fluctuated between levels (restricted, unrestricted, and ineligible). The results are presented in Tables 17 - 24.





Table 17. Relative Risk for Citations, Single Functional Ability Category and Corresponding Comparison Groups by One Restriction Status, Utah 1992 1996

Condition

Restriction Status

Medical Conditions

Comparison Group

Rate Ratio

Drivers

Citations

# Days

Rate

Comparisons

Citation

# Days

Rate

Ratio

L 95%

U 95%

Significance

Diabetes

Not Restricted

9,731

2,478

9,616,680

2.58

18,985

7,537

29,844,852

2.53

1.02

0.98

1.07

 

 

Restricted

31

3

9,117

3.29

62

25

97,383

2.57

1.28

0.39

4.23

 

Cardiovascular

Not Restricted

18,865

1,422

11,538,711

1.23

34,510

9,578

59,072,515

1.62

0.76

0.72

0.80

**

 

Restricted

41

6

9,827

6.11

82

21

129,305

1.62

3.76

1.62

8.75

*

Pulmonary

Not Restricted

2,437

425

1,816,080

2.34

4,844

1,930

7,273,732

2.65

0.88

0.79

0.98

**

 

Restricted

69

0

23,115

0.00

138

29

197,671

1.47

zero rate

 

 

 

Neurologic

Not Restricted

773

119

572,607

2.08

1,545

551

2,371,934

2.32

0.89

0.73

1.09

 

 

Restricted

79

4

45,676

0.88

158

47

241,288

1.95

0.45

0.17

1.21

 

Epilepsy

Not Restricted

1,893

768

1,992,785

3.85

3,775

2,212

5,632,320

3.93

0.98

0.90

1.07

 

 

Restricted

71

15

22,518

6.66

142

48

205,728

2.33

2.86

1.64

4.97

*

Learning

Not Restricted

102

31

62,973

4.92

204

107

281,642

3.80

1.30

0.87

1.93

 

 

Restricted

3

0

1,182

0.00

6

0

7,285

0.00

zero rate

 

 

 

Psychiatric

Not Restricted

6,481

1,932

5,027,373

3.84

12,838

6,187

19,527,510

3.17

1.21

1.15

1.28

*

 

Restricted

42

3

14,799

2.03

84

52

125,506

4.14

0.49

0.16

1.53

 

Alcohol

Not Restricted

124

67

77,740

8.62

248

139

376,058

3.70

2.33

1.76

3.09

*

 

Restricted

5

5

2,506

19.95

10

10

15,382

6.50

3.07

1.11

8.50

*

Vision

Not Restricted

10,116

1,247

4,191,935

2.97

19,287

6,518

29,517,765

2.21

1.35

1.27

1.43

*

 

Restricted

1,279

142

781,209

1.82

2,479

514

3,672,929

1.40

1.30

1.08

1.56

*

Musculoskeletal

Not Restricted

353

52

214,610

2.42

705

210

1,092,772

1.92

1.26

0.93

1.71

 

 

Restricted

15

0

4,803

0.00

30

10

44,663

2.24

zero rate

 

 

 

Functional Motor

Not Restricted

208

44

143,549

3.07

416

143

638,279

2.24

1.37

0.98

1.92

 

 

Restricted

8

0

4,125

0.00

14

5

23,558

2.12

zero rate

 

 

 

Rates are expressed as citations per 10,000 license days.





Table 18. Relative Risk for Citations, Single Functional Ability Category and Corresponding Comparison Groups by Fluctuating Restriction Status, Utah 1992 1996

Condition

Restriction Status

Medical Conditions

Comparison Group

Rate Ratio

Drivers

Citations

# Days

Rate

Comparison

Citations

# Days

Rate

Ratio

L 95%

U 95%

Significance

Diabetes

Not Restricted

338

122

334,513

3.65

676

327

990,416

3.30

1.10

0.90

1.36

 

 

Restricted

327

21

45,082

4.66

654

312

956,944

3.26

1.43

0.92

2.22

 

Cardiovascular

Not Restricted

125

6

80,496

0.75

250

83

388,291

2.14

0.35

0.16

0.77

**

 

Restricted

119

1

12,463

0.80

238

78

369,733

2.11

0.38

0.06

2.54

 

Pulmonary

Not Restricted

178

13

137,498

0.95

356

79

565,921

1.40

0.68

0.38

1.21

 

 

Restricted

175

4

34,649

1.15

350

78

557,100

1.40

0.82

0.30

2.25

 

Neurologic

Not Restricted

114

19

81,262

2.34

228

75

343,436

2.18

1.07

0.65

1.77

 

 

Restricted

115

11

46,006

2.39

230

80

347,338

2.30

1.04

0.55

1.95

 

Epilepsy

Not Restricted

727

300

634,584

4.73

1,452

852

2,087,279

4.08

1.16

1.02

1.32

*

 

Restricted

704

47

127,462

3.69

1,406

824

2,016,155

4.09

0.90

0.67

1.21

 

Learning

Not Restricted

5

1

3,492

2.86

10

7

16,512

4.24

0.68

0.08

5.42

 

 

Restricted

3

4

763

52.42

6

3

9,678

3.10

16.91

5.66

50.51

*

Psychiatric

Not Restricted

282

149

259,940

5.73

564

325

870,254

3.73

1.53

1.27

1.86

*

 

Restricted

263

16

43,648

3.67

526

309

808,693

3.82

0.96

0.58

1.59

 

Alcohol

Not Restricted

19

7

9,724

7.20

38

16

60,511

2.64

2.72

1.16

6.38

*

 

Restricted

19

7

3,498

20.01

38

16

60,511

2.64

7.57

3.56

16.07

*

Vision

Not Restricted

247

22

100,633

2.19

491

94

698,075

1.35

1.62

1.09

2.42

*

 

Restricted

256

15

91,290

1.64

508

90

717,900

1.25

1.31

0.95

1.81

 

Musculoskeletal

Not Restricted

17

1

10,365

0.96

34

12

57,068

2.10

0.46

0.06

3.35

 

 

Restricted

17

0

4,211

0.00

34

12

57,068

2.10

zero rate

 

 

 

Functional Motor

Not Restricted

6

7

4,044

17.31

12

18

21,482

8.38

2.07

0.61

7.04

 

 

Restricted

5

0

1,244

0.00

10

7

17,828

3.93

zero rate

 

 

 

Rates are expressed as citations per 10,000 license days.

*The confidence interval does not include 1.0. Therefore, the higher rate of the medical conditions group is statistically significant.

** indicates that the medical conditions group has a statistically significant lower rate.







Table 19. Relative Risk for Crashes, Single Functional Ability Category and Corresponding Comparison Groups by Single Restriction Status, Utah 1992 1996

Condition

Restriction Status

Medical Conditions

Comparison Group

Rate Ratio

Drivers

Crashes

# Days

Rate

Comparison

Crashes

# Days

Rate

Ratio

L 95%

U 95%

Significance

Diabetes

Not Restricted

9,731

1,611

9,616,680

1.68

18,985

3,873

29,844,852

1.30

1.29

1.22

1.37

*

 

Restricted

31

1

9,117

1.10

62

11

97,383

1.13

0.97

0.13

7.52

 

Cardiovascular

Not Restricted

18,865

1,203

11,538,711

1.04

34,510

6,198

59,072,515

1.05

0.99

0.93

1.06

 

 

Restricted

41

3

9,827

3.05

82

17

129,305

1.31

2.32

0.71

7.65

 

Pulmonary

Not Restricted

2,437

281

1,816,080

1.55

4,844

944

7,273,732

1.30

1.19

1.04

1.36

*

 

Restricted

69

1

23,115

0.43

138

17

197,671

0.86

0.50

0.07

3.63

 

Neurologic

Not Restricted

773

106

572,607

1.85

1,545

282

2,371,934

1.19

1.56

1.25

1.94

*

 

Restricted

79

4

45,676

0.88

158

37

241,288

1.53

0.57

0.21

1.58

 

Epilepsy

Not Restricted

1,893

501

1,992,785

2.51

3,775

825

5,632,320

1.46

1.72

1.54

1.92

*

 

Restricted

71

5

22,518

2.22

142

33

205,728

1.60

1.38

0.54

3.53

 

Learning

Not Restricted

102

19

62,973

3.02

204

44

281,642

1.56

1.93

1.14

3.28

*

 

Restricted

3

0

1,182

0.00

6

0

7,285

0.00

zero rate

 

 

 

Psychiatric

Not Restricted

6,481

1,115

5,027,373

2.22

12,838

2,809

19,527,510

1.44

1.54

1.44

1.65

*

 

Restricted

42

5

14,799

3.38

84

25

125,506

1.99

1.70

0.66

4.38

 

Alcohol

Not Restricted

124

22

77,740

2.83

248

58

376,058

1.54

1.83

1.13

2.98

*

 

Restricted

5

2

2,506

7.98

10

2

15,382

1.30

6.14

1.10

34.10

*

Vision

Not Restricted

10,116

735

4,191,935

1.75

19,287

3,851

29,517,765

1.30

1.34

1.24

1.45

*

 

Restricted

1,279

110

781,209

1.41

2,479

399

3,672,929

1.09

1.30

1.05

1.60

*

Musculoskeletal

Not Restricted

353

37

214,610

1.72

705

115

1,092,772

1.05

1.64

1.14

2.36

*

 

Restricted

15

0

4,803

0.00

30

1

44,663

0.22

zero rate

 

 

 

Functional Motor

Not Restricted

208

20

143,549

1.39

416

88

638,279

1.38

1.01

0.62

1.75

 

 

Restricted

8

0

4,125

0.00

14

5

23,558

2.12

Zero Rate

 

 

 

Rates are expressed as crashes per 10,000 license days.

*The confidence interval does not include 1.0. Therefore, the higher rate of the medical conditions group is statistically significant.

** indicates that the medical conditions group has a statistically significant lower rate.






Table 20. Relative Risk for Crashes, Single Functional Ability Category and Corresponding Comparison Groups by Fluctuating Restriction Status, Utah 1992 1996


Condition

Restriction Status

Medical Conditions

Comparison Group

Rate Ratio

Drivers

Crashes

# Days

Rate

Comparison

Crashes

# Days

Rate

Ratio

L 95%

U 95%

Significance

Diabetes

Not Restricted

338

82

334,513

2.45

676

150

990,416

1.51

1.62

1.24

2.11

*

 

Restricted

327

10

45,082

2.22

654

144

956,944

1.50

1.47

0.78

2.79

 

Cardiovascular

Not Restricted

125

6

80,496

0.75

250

35

388,291

0.90

0.83

0.35

1.96

 

 

Restricted

119

0

12,463

0.00

238

32

369,733

0.87

zero rate

 

 

 

Pulmonary

Not Restricted

178

16

137,498

1.16

356

69

565,921

1.22

0.95

0.55

1.64

 

 

Restricted

175

5

34,649

1.44

350

69

557,100

1.24

1.17

0.47

2.89

 

Neurologic

Not Restricted

114

18

81,262

2.22

228

36

343,436

1.05

2.11

1.22

3.67

*

 

Restricted

115

12

46,006

2.61

230

40

347,338

1.15

2.26

1.21

4.24

*

Epilepsy

Not Restricted

727

207

634,584

3.26

1,452

375

2,087,279

1.80

1.82

1.54

2.15

*

 

Restricted

704

35

127,462

2.75

1,406

370

2,016,155

1.84

1.50

1.06

2.11

*

Learning

Not Restricted

5

3

3,492

8.59

10

1

16,512

0.61

14.19

2.55

78.79

*

 

Restricted

3

1

763

13.11

6

0

9,678

0.00

zero rate

 

 

 

Psychiatric

Not Restricted

282

69

259,940

2.65

564

108

870,254

1.24

2.14

1.59

2.87

*

 

Restricted

263

10

43,648

2.29

526

103

808,693

1.27

1.80

0.95

3.41

 

Alcohol

Not Restricted

19

5

9,724

5.14

38

16

60,511

2.64

1.94

0.73

5.21

 

 

Restricted

19

4

3,498

11.44

38

16

60,511

2.64

4.32

1.59

11.80

*

Vision

Not Restricted

247

18

100,633

1.79

491

80

698,075

1.15

1.56

0.94

2.59

 

 

Restricted

256

12

91,290

1.31

508

85

717,900

1.18

1.11

0.61

2.03

 

Musculoskeletal

Not Restricted

17

0

10,365

0.00

34

4

57,068

0.70

zero rate

 

 

 

 

Restricted

17

2

4,211

4.75

34

4

57,068

0.70

6.78

1.57

29.29

*

Functional Motor

Not Restricted

6

3

4,044

7.42

12

5

21,482

2.33

0.90

0.80

1.02

 

 

Restricted

5

0

1,244

0.00

10

2

17,828

1.12

zero rate

 

 

 

Rates are expressed as crashes per 10,000 license days.

*The confidence interval does not include 1.0. Therefore, the higher rate of the medical conditions group is statistically significant.

** indicates that the medical conditions group has a statistically significant lower rate.






Table 21. Relative Risk for At-Fault Crashes, Single Functional Ability Category and Corresponding Comparison Groups by Single Restriction Status, Utah 1992 1996

Condition

Restriction Status

Medical Conditions

Comparison Group

Rate Ratio

Condition

Crashes

# Days

Rate

Comparisons

Crashes

# Days

Rate

Ratio

L 95%

U 95%

Significance

Diabetes

Not Restricted

9,731

957

9,616,680

1.00

18,985

2,058

29,844,852

0.69

1.44

1.34

1.56

*

 

Restricted

31

1

9,117

1.10

62

3

97,383

0.31

3.56

0.43

29.60

 

Cardiovascular

Not Restricted

18,865

635

11,538,711

0.55

34,510

3,239

59,072,515

0.55

1.00

0.92

1.09

 

 

Restricted

41

2

9,827

2.04

82

14

129,305

1.08

1.88

0.44

8.07

 

Pulmonary

Not Restricted

2,437

155

1,816,080

0.85

4,844

496

7,273,732

0.68

1.25

1.05

1.50

*

 

Restricted

69

1

23,115

0.43

138

12

197,671

0.61

0.71

0.09

5.43

 

Neurologic

Not Restricted

773

72

572,607

1.26

1,545

142

2,371,934

0.60

2.10

1.59

2.77

*

 

Restricted

79

4

45,676

0.88

158

22

241,288

0.91

0.96

0.33

2.79

 

Epilepsy

Not Restricted

1,893

305

1,992,785

1.53

3,775

464

5,632,320

0.82

1.86

1.61

2.14

*

 

Restricted

71

5

22,518

2.22

142

16

205,728

0.78

2.86

1.09

7.45

*

Learning

Not Restricted

102

14

62,973

2.22

204

23

281,642

0.82

2.72

1.44

5.15

*

 

Restricted

3

0

1,182

0.00

6

0

7,285

0.00

zero rate

 

 

 

Psychiatric

Not Restricted

6,481

678

5,027,373

1.35

12,838

1,464

19,527,510

0.75

1.80

1.64

1.97

*

 

Restricted

42

4

14,799

2.70

84

17

125,506

1.35

2.00

0.69

5.80

 

Alcohol

Not Restricted

124

13

77,740

1.67

248

27

376,058

0.72

2.33

1.23

4.43

*

 

Restricted

5

2

2,506

7.98

10

2

15,382

1.30

6.14

1.10

34.10

*

Vision

Not Restricted

10,116

479

4,191,935

1.14

19,287

2,228

29,517,765

0.75

1.51

1.37

1.67

*

 

Restricted

1,279

93

781,209

1.19

2,479

274

3,672,929

0.75

1.60

1.26

2.01

*

Musculoskeletal

Not Restricted

353

22

214,610

1.03

705

59

1,092,772

0.54

1.90

1.17

3.07

*

 

Restricted

15

0

4,803

0.00

30

0

44,663

0.00

zero rate

 

 

 

Functional Motor

Not Restricted

208

17

143,549

1.18

416

42

638,279

0.66

1.80

1.03

3.14

*

 

Restricted

8

0

4,125

0.00

14

3

23,558

1.27

zero rate

 

 

 

Rates are expressed as crashes per 10,000 license days.

*The confidence interval does not include 1.0. Therefore, the higher rate of the medical conditions group is statistically significant.

** indicates that the medical conditions group has a statistically significant lower rate.






Table 22. Relative Risk for At-Fault Crashes, Single Functional Ability Category and Corresponding Comparison Groups by Fluctuating Restriction Status, Utah 1992 1996

Condition

Restriction Status

Medical Conditions

Comparison Group

Rate Ratio

Drivers

Crashes

# Days

Rate

Comparison

Crashes

# Days

Rate

Ratio

L 95%

U 95%

Significance

Diabetes

Not Restricted

338

56

334,513

1.67

676

88

990,416

0.88

1.88

1.36

2.62

*

 

Restricted

327

7

45,082

1.55

654

85

956,944

0.88

1.75

0.82

3.74

 

Cardiovascular

Not Restricted

125

2

80,496

0.25

250

17

388,291

0.44

0.57

0.13

2.41

 

 

Restricted

119

0

12,463

0.00

238

15

369,733

0.41

zero rate

 

 

 

Pulmonary

Not Restricted

178

12

137,498

0.87

356

37

565,921

0.64

1.33

0.70

2.55

 

 

Restricted

175

5

34,649

1.44

350

37

557,100

0.65

2.17

0.87

5.40

 

Neurologic

Not Restricted

114

14

81,262

1.72

228

20

343,436

0.52

2.96

1.54

5.67

*

 

Restricted

115

6

46,006

1.30

230

24

347,338

0.63

1.89

0.78

4.55

 

Epilepsy

Not Restricted

727

158

634,584

2.49

1,452

209

2,087,279

0.96

2.49

2.04

3.04

*

 

Restricted

704

31

127,462

2.43

1,406

207

2,016,155

0.98

2.37

1.64

3.42

*

Learning

Not Restricted

5

3

3,492

8.59

10

0

16,512

0.00

zero rate

 

 

 

 

Restricted

3

1

763

13.11

6

0

9,678

0.00

zero rate

 

 

 

Psychiatric

Not Restricted

282

49

259,940

1.89

564

56

870,254

0.63

2.93

2.03

4.22

*

 

Restricted

263

9

43,648

2.06

526

55

808,693

0.67

3.03

1.55

5.92

*

Alcohol

Not Restricted

19

3

9,724

3.09

38

9

60,511

1.49

2.07

0.58

7.45

 

 

Restricted

19

3

3,498

8.58

38

9

60,511

1.49

5.77

1.82

18.27

*

Vision

Not Restricted

247

14

100,633

1.39

491

52

698,075

0.70

1.87

1.02

3.42

*

 

Restricted

256

9

91,290

0.99

508

55

717,900

0.72

1.29

0.54

3.09

 

Musculoskeletal

Not Restricted

17

0

10,365

0.00

34

2

57,068

0.35

zero rate

 

 

 

 

Restricted

17

2

4,211

4.75

34

2

57,068

0.35

13.55

0.04

4790.38

 

Functional Motor

Not Restricted

6

1

4,044

2.47

12

5

21,482

1.86

1.06

0.95

1.18

 

 

Restricted

5

0

1,244

0.00

10

2

17,828

0.56

zero rate

 

 

 



Rates are expressed as crashes per 10,000 license days.

*The confidence interval does not include 1.0. Therefore, the higher rate of the medical conditions group is statistically significant.

** indicates that the medical conditions group has a statistically significant lower rate.





Table 23. Relative Risk for Adverse Driving Events, Drivers with Multiple Medical Conditions and Corresponding Comparison Groups by Single Restriction Status, Utah 1992 1996

 

Restriction Status

Medical Conditions

Comparison Group

Rate Ratio

Drivers

# Events

# Days

Rate

Comparison

# Events

# Days

Rate

Ratio

L 95%

U 95%

Significance

Citation

Not Restricted

11,270

1,747

10,690,248

1.63

21,277

6,012

34,910,617

1.72

0.95

0.90

1.00

 

 

Restricted

372

27

179,083

1.51

740

216

1,093,426

1.98

0.76

0.51

1.14

 

Crash

Not Restricted

11,270

1,630

10,690,248

1.52

21,277

3,903

34,910,617

1.12

1.36

1.29

1.45

*

 

Restricted

372

31

179,083

1.73

740

128

1,093,426

1.17

1.48

1.001

2.18

*

At Fault Crash

Not Restricted

11,270

992

10,690,248

0.93

21,277

2,115

34,910,617

0.61

1.53

1.42

1.65

*

 

Restricted

372

27

179,083

1.51

740

62

1,093,426

0.57

2.66

1.72

4.11

*

Rates are expressed as events per 10,000 license days.

*The confidence interval does not include 1.0. Therefore, the higher rate of the medical conditions group is statistically significant.

** indicates that the medical conditions group has a statistically significant lower rate.






Table 24. Relative Risk for Adverse Driving Events, Drivers with Multiple Medical Conditions and Corresponding Comparison Groups by Fluctuating Restriction Status, Utah 1992 1996

 

Restriction Status

Medical Conditions

Comparison Group

Rate Ratio

Drivers

# Events

# Days

Rate

Comparison

# Events

# Days

Rate

Ratio

L 95%

U 95%

Significance

Citation

Not Restricted

2,138

375

1,740,644

2.15

4,219

1,212

6,518,846

1.86

1.15

1.03

1.30

*

 

Restricted

2,042

73

482,944

1.51

4,034

1,164

6,228,833

1.87

0.81

0.64

1.02

 

Crash

Not Restricted

2,138

335

1,740,644

1.92

4,219

756

6,518,846

1.16

1.66

1.46

1.88

*

 

Restricted

2,042

66

482,944

1.37

4,034

712

6,228,833

1.14

1.20

0.93

1.54

 

At Fault Crash

Not Restricted

2,138

237

1,740,644

1.36

4,219

452

6,518,846

0.69

1.96

1.68

2.29

*

 

Restricted

2,042

46

482,944

0.95

4,034

421

6,228,833

0.68

1.41

1.04

1.91

*

Rates are expressed as events per 10,000 license days.

*The confidence interval does not include 1.0. Therefore, the higher rate of the medical conditions group is statistically significant.

** indicates that the medical conditions group has a statistically significant lower rate.












DISCUSSION

In this study, we have determined the rates of citations, crashes and at fault crashes of drivers licensed in the medical conditions program and compared them to the rates of demographically similar drivers. Our study describes the driving performance of drivers who report their medical conditions to the licensing agency. It does not describe how medical conditions influence driving performance directly. Additionally, this study describes how the licensing program for drivers with medical conditions works in Utah, and provides demographic information about the population that participates in this public safety program.

The effects of medical conditions on drivers' performance has been the subject of many research reports. However, there is little published information on the effects of specialized licensing programs that regulate such drivers . Our study is unique in its approach to evaluating the effects of a statewide licensing program for drivers with such medical conditions. Utah CODES was able to evaluate the rates of 68,770 drivers licensed in the state with medical conditions by category and restriction status for a five year period using probabilistically linked data. To date, this is the most comprehensive evaluation of such a statewide medical conditions licensing program. The information gained from these data analyses can be used by regulatory agencies such as the Utah Driver License Division to improve the existing program.

Approximately 80% (54,938) of the study population reported a single medical condition for the study period. Overall, all single medical condition unrestricted drivers had higher rates for all three events (citation, crash and at fault crash) than their corresponding comparison group. Restricted drivers (e.g., time, speed, area) reporting single medical conditions had higher rates for crash and at-fault crash than their comparison groups, but a similar rate of citation. That is, restrictions led to equivalent citation rates but did not have the same effect on crash rates.

There was great variability when analyses were performed for each medical condition by restriction status. Some categories had higher rates of some or all of the adverse driving events. Others had similar or even lower rates of these events when compared to their comparison groups. These differences imply that there is a relationship between the drivers' type(s) of medical conditions and the rates of adverse driving events. Furthermore, these differences quantify the outcome of the existing medical conditions program, and provide indications for changes to improve public safety. It should be noted however, that our measurement for restricted drivers only includes about half of the drivers who were restricted; approximately half of the drivers who were restricted of the total study population had multiple medical conditions. Therefore, they were analyzed separately as multiple condition drivers.

We found that drivers licensed in certain medical condition categories pose a greater hazard when driving as shown by their higher rates of adverse driving events when compared to their comparisons. Categories showing consistently higher rates for all three events (citation, crash and at fault crash) included:

  1. unrestricted medical condition drivers in the "psychiatric and emotional conditions" category
  2. restricted and unrestricted drivers in the "alcohol and other drugs" category, and
  3. restricted and unrestricted "vision" category drivers.

Categories where only crash and at fault crash rates were higher than those of the comparison drivers included:

  1. unrestricted drivers in the "diabetes and other metabolic conditions" category
  2. unrestricted drivers in the "pulmonary conditions" category
  3. unrestricted drivers in the "neurological conditions" category
  4. unrestricted and restricted drivers in the "epilepsy and other episodic conditions" category
  5. unrestricted drivers in the "learning, memory and communication disorders" category,
  6. restricted drivers in the "psychiatric and emotional conditions" category, and the
  7. unrestricted and restricted drivers in the "musculoskelatal abnormality or chronic medical debility" category.

We have presented a degree of risk for each category as a relative risk. This is a ratio of the rates of events that compare medical condition drivers to the rates of comparison drivers. While this ratio quantifies adverse driving events for medical condition populations to demographically similar drivers, the rates of events themselves are also of interest. Functional ability groups with high relative risks, but low rates, probably do not have a great adverse impact on public safety. Thus, the risk caused by these groups may not warrant changes to this safety program.

The stratified analyses presented in Tables 17-24, show that there was no difference between drivers licensed with single medical conditions who fluctuated between licensing levels, and those whose restriction status remained the same for all functional ability categories. The confidence levels for those who fluctuate and those in a single restriction status overlap. However, this is not the case for those drivers in multiple functional ability categories: Drivers whose restriction status fluctuated and were licensed with multiple conditions during the period had a higher risk for all three adverse driving than those who remained at a single restriction level throughout the study period, when compared to their respective comparison groups.

A logical conjecture may be to compare the results of restricted drivers to the results for unrestricted drivers as ascribed to the effects of the program's restrictions. In essence, it seems reasonable to create a ratio of ratios for restricted vs. unrestricted drivers. We have considered such an analysis, but have elected not to do so. Such a comparison may lead to the incorrect assumption that the differences are because of the program only. Drivers who are restricted may have much different exposure rates because of the program itself, or because of their illness(es) or condition(s). By nature of the licensing program, restricted drivers are more medically fragile and unstable, depending upon their conditions. Moreover, the question of comparing similar groups arises when evaluating these restricted drivers. The activity and fitness level of elderly persons, most of which comprise restricted drivers, varies greatly; accordingly, so would their driving exposures and performance.

The analyses provided in this report describe the effects of a statewide licensing program for drivers with medical conditions. There are, however, several limitations that must be considered when evaluating these results. Among the first, is that the accurate measurements of exposure and other factors that affect the risk of citation or crash are not available. We assumed that the amount and conditions of driving for persons with medical conditions could be best estimated by selecting comparisons using age group, county of residence, and sex. This may in fact be incorrect, as other factors influence the amount people drive. They include marital and economic status, employment, higher education, being a member of a social or religious organization, and residential demographics . Similarly, the rates determined in the study could be influenced by a small number of drivers who had repeat crashes and/or citations during the study period. Thus, a specific analysis to identify drivers with repeat offenses should be performed.

In addition to uncertainty about exposure rates as noted above, other factors, currently impossible to assess, might also confound the program. For instance, we assumed that the drivers complied with the program as designed (although this is not a limitation of our study, rather of the medical conditions program itself). However, drivers initially assigned restrictions might have "doctor-shopped" to acquire a more favorable rating. The Utah Driver License Division has speculated that applicants who are initially assigned a high functional ability level may visit different health care providers until they receive a lower functional ability level. Thus, drivers who should receive a restricted license because of their medical conditions may receive a lower (levels 3-5) functional ability level, and thus an unrestricted driver license. Also, applicants who should be ineligible for a driver license may visit different health care professionals until they receive a functional ability assignment that will allow them a license. It is unknown whether or not health care professionals assign functional ability levels according to the system. Compliance with the program for restricted drivers (e.g., time, area or speed) was also assumed. For example, while some restricted drivers are not supposed to drive after dark because of the restrictions placed upon their driver licenses, we did not verify that these drivers were following their restrictions at the time of the crash or citation.

The proportion of drivers who have medical conditions that report their conditions to the Utah Driver License Division is unknown. The presented results are the results of the program as it has functioned during 1992 - 1995. These results cannot be applied to all drivers who have medical conditions. As described previously, the Utah Driver License Division screens license applicants for medical conditions through a general questionnaire using self report. There is no incentive for applicants to report a medical condition since doing so may require a longer wait for a driver license or a visit to a health care professional. This lack of reporting has been described previously; Medgyesi and Koch showed that for every driver with a cardiovascular disease known to the licensing division through its medical review program, there were 94 drivers who were unknown in Saskatchewan, Canada . We estimate that in Utah, reporting compliance is somewhat better than those aforementioned, but far from complete. Compliance obviously varies by medical category. For example, the Utah Department of Health estimates that the prevalence of diabetes was 2.9% (57,900) of the general population in 1996 . Less than half (26,458, 46%) of these persons, although not all would be licensed drivers, reported their condition to the driver license division. Additionally, Medgyesi and Koch suggest that drivers who report their medical conditions to licensing authorities do so because they are very poor drivers, even worse than drivers with medical conditions who do not report their conditions . If this is the case in Utah, applying these estimates of risk to all drivers with medical conditions would be inaccurate.











RECOMMENDATIONS

The determination of citation, crash and at fault crash rates by functional ability category and the corresponding estimates of relative risk provide useful information for the evaluation of the existing medical conditions program in Utah. The results of this study indicate where the citation and crash risk for the medical condition population exceeds the risk for the general population.

It is important that the information gained by this study regarding this licensing program be interpreted correctly in light of the study's existing limitations. It is difficult to attribute the reasons for the differences in the crash and violation rates of the medical conditions and general driving populations. This does not mean that the existing program is not beneficial to public safety. The results indicate that participation in the program does not completely negate the effects of the medical condition related to driving. Accordingly, the existing program should be changed in order to reduce the excess risk of drivers with medical conditions to approximate the risks of the general driving population. Further analyses may be necessary to make specific recommendations for reducing risks by specific functional ability categories. However, general recommendations can be made in order to provide a framework for improving the current system. They include:

Efforts to modify the existing program should be prioritized by the Utah Driver License Division and the Utah Medical Advisory Board. Additionally, these agencies should work together to determine the range, scope and order of future research that is necessary to develop the appropriate modifications specific to each functional ability category. Consideration should also be given to this study's existing limitations described in the previous section.

Factors that should be considered when prioritizing functional ability categories should include the rates for events of concern, the estimates of risk and the size of the functional ability category population. An incremental approach to modifying the system is suggested. Priority should be placed on those functional ability categories where the risk for events of concern approaches or exceeds the risk for the comparison populations by a factor of 2.0 where statistical significance is achieved, and where the rates of the events themselves are high. When the relative risk exceeds 2.0, it may be interpreted that the rate of the event exceeds that of the corresponding comparison group by at least 2.0 times. While this factor has been arbitrarily chosen, it represents an estimate of difference between the licensed populations and their effect on public safety. Moreover, this limit of 2.0 affects only two citation categories (i.e., learning, and alcohol and other drugs) and six crash categories (i.e., neurologic; epilepsy; learning, memory and communication disorders, psychiatric and other emotional conditions, alcohol and other drugs; and musculoskelatal). The functional ability categories of learning, memory and communication and alcohol and other drugs had very high rates; the citation rates for restricted categories were 20.57 and 19.99 per 100,000 license days.

Priorities should be placed on functional ability categories that had smaller estimates of statistically significant risks but larger populations (i.e., vision). By slightly reducing the risk for a larger number of drivers, the benefit to public safety may be even greater than reducing a large risk for a small number of persons. Functional ability categories that fall into this description include diabetes and other metabolic conditions, visual acuity and psychiatric and emotional conditions.

All modifications should be tailored to the individual functional ability category. As mentioned previously, additional research may benefit from being tailored to the specific functional ability category. For example, the "alcohol and other drugs" category has high rates for restricted and unrestricted drivers for most events. There are three functional ability levels that allow for an unrestricted license: 3. history of drug abuse but not in the past five years; 4. history of drug abuse but not within the past two years; or 5. history of drug abuse but not in the past six months. Further analyses should include an evaluation of whether substance abuse was involved in any of these adverse driving events to determine if the licensing program is being followed. If not, a quality loop could be developed such as having all alcohol or drug related citations/crashes being reported to the program administrators. Additionally, specific analyses should be performed by individual functional ability level to determine if the rate differences between these levels provide indications on how to structure changes to the program.

Examples include analyzing the crash environment to determine if there are risk factors that could be negated with more appropriate restrictions, or modeling of drivers by specific functional ability levels to determine whether the restriction boundary should be inserted at a different place.

The Utah Driver License Division would benefit from simplifying the existing program where possible. This recommendation is made particularly in regards to the system where there are twelve functional ability levels available for each functional ability or medical condition category. Although functional ability categories with large numbers of drivers (e.g., diabetes and other metabolic conditions or cardiovascular conditions) may benefit from having twelve different categories, functional ability categories having a small number of drivers (e.g., learning, memory and communications or alcohol and other drugs) do not. Such levels only increase the administrative burden without measurable benefit to the program.

Further analyses should be performed for drivers with multiple conditions, and common combinations of multiple conditions. As described in the results, there were 13,832 drivers who had multiple functional ability categories during the study period. Of those, certain medical condition combinations (i.e., cardiovascular and diabetes, cardiovascular and vision, cardiovascular and pulmonary) are more common than separate categories with small numbers of drivers. Further analyses should be performed to evaluate the effects of these multiple condition combinations. It may be practical to develop multiple condition categories for large groups with comorbid conditions, rather than to fit them into two separate categories.

Relational files should be utilized instead of the existing flat system for recordkeeping. The existing files were difficult to analyze because a new record was entered for each medical condition every time the driver renewed his or her license. This database format made it particularly difficult to analyze the rates of drivers with multiple medical conditions.

Finally, any modifications to the existing program should be carefully documented. Because of the nature of the medical condition program, changes would be implemented over time. Thus, careful documentation of the date of implementation on an individual level (i.e., the renewal date for the license holder when he/she is affected by the changes) is required in order to evaluate the effects of such changes. Accordingly, the effects of changes implemented on rates of events and estimates of risk should be measured to assure that they are of benefit to public safety.

Driver license agencies, as regulatory entities, have the responsibility of developing and enforcing policies that protect public safety, while balancing the risks of licensing drivers who have physical or mental impairments. Utah is not unique in the development and implementation of a licensing program for drivers with medical conditions; most states have specific policies related to physical and mental function and driving . The rationale for such programs is that certain diseases or conditions could impair driving ability and, therefore, drivers with medical conditions should be subject to a more rigorous screening process so that they do not jeopardize others on the roads . Any such program, however, must be applied in a careful and reasonable fashion; note that it is unlawful for any State or local government under the Americans with Disabilities Act to discriminate against a qualified person with disabilities on the basis of those disabilities.

Because of the demographic shift in the age of our population , and the higher prevalence of chronic medical conditions in elderly persons, it is increasingly important to evaluate the effects of these existing programs and to assure that they are protective of public safety as is their intent. The number of drivers in these programs will only increase in future years and modifications resulting from such analyses, can prove future benefit.











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