PROGRAM RESULTS

The primary measures of program effects for this evaluation of aggressive driving countermeasures are, 1) samples of vehicle speeds, and 2) the incidence of crashes in the special enforcement zones. Program results are presented in these two categories in the following paragraphs.

SPEED SAMPLES
One-hour samples of vehicle speed were taken unobtrusively at the same locations, beginning at least one month prior to program implementation. Speed samples were obtained by use of lidar devices at the same locations, during the same weeks of the month, and for each location, on the same day of the week and the same hour of the day (to maximize comparability). Data collectors were instructed to postpone sampling one week if it appeared that rain at a scheduled sampling time would affect vehicle speeds. Program personnel in Marion County and Tucson interpreted the speed sample requirement differently, resulting in non-uniform baseline periods and slightly different sampling schedules. However, data collectors for both programs followed the same sampling procedures and used identical data collection forms.

MARION COUNTY SPEED SAMPLE RESULTS
The Marion County special enforcement program was conducted from March 1 through August 31, 2001. Program personnel collected speed samples at five locations, beginning approximately three months prior to the start of the program and continuing throughout the six-month program period. Samples consisted of 105 vehicle speeds for each location and date. Data collection forms were sent to Anacapa Sciences, Inc., for data entry and analysis. The following three figures, collectively labeled as Figure 4, illustrate the results of the analysis, presenting the average vehicle speed and the highest speed recorded on each sampling date; the shaded areas indicate the baseline period (i.e., samples taken prior to program implementation). Each figure represents a separate sampling location. Marion County began with five special enforcement zones, but program managers abandoned locations A and E mid-way through the program.

Table 3 summarizes the speed sample results illustrated in the figures. The table shows that average speeds during the program period were slightly lower than during the baseline periods at two of the sites, and slightly higher at the third sites. The average of the averages shows a one percent decline in speed, overall. However, this calculation could be misleading if the different posted speed limits at the locations differentially influence drivers’ responses to the special enforcement program; although this does not appear to be the case, averages of averages could obscure program effects.7 For this reason, an alternative measure is to sum the percent change values for the three sampling sites that were within the program’s three special enforcement zones: Site B declined by one percent, Site C declined by three percent, and Site D increased by one percent, for an overall decline in average speed of three percentage points in Marion County’s special enforcement zones.

Figure 4. Marion County speed sample results.

TABLE 3
MARION COUNTY UNOBTRUSIVE SPEED SAMPLES:
COMPARISON OF AVERAGE OF BASELINE SAMPLES TO
AVERAGE OF SAMPLES DURING THE PROGRAM PERIOD, IN MILES PER HOUR

Site
SpeedLimit
Average Speed
Baseline Period
Average Speed
Program Period
Percent
Change
B
40
45.68
45.03
-1%
C
35
41.67
40.62
-3%
D
35
40.50
41.02
+1%
Average of All 3 Sites
42.62
42.22
-1%
Sum of Change Values
-3%

TUCSON SPEED SAMPLE RESULTS
The Tucson special enforcement program was conducted from July 1 through December 31, 2001. Program personnel collected speed samples at four locations, beginning in January and continuing throughout the six-month program period. Samples consisted of between 686 and 1,274 vehicle speeds for each location and date. Data were entered by program personnel and sent to Anacapa Sciences, Inc., for analysis. The following four figures, collectively labeled as Figure 5, illustrate the results of the analysis, presenting the average vehicle speed and the highest speed recorded on each sampling date; the shaded areas indicate the baseline period (i.e., samples taken prior to program implementation). Each figure represents a separate sampling location. Each location was within one of the four zones on which the Tucson Police Department focused its special enforcement efforts.

Table 4 summarizes the speed sample results illustrated in the figures. The table shows that average speeds during the program period were slightly higher than during the baseline periods at one of the sites, slightly lower at two of the sites, and substantially lower at one of the sites. The average of the averages shows a three percent decline in speed, overall. But, as before, calculating the averages of averages could obscure program effects. Summing the percent change values for the four sampling sites, all of which were within the program’s four special enforcement zones, again provides a more appropriate measure: Site 1 declined by nine percent, Site 2 declined by three percent, Site 3 increased by one percent, and Site 4 declined by two percent, for an overall decline in average speed of 13 percentage points in Tucson’s special enforcement zones.

Figure 5. Tucson speed sample results.

TABLE 4
TUCSON UNOBTRUSIVE SPEED SAMPLES:
COMPARISON OF AVERAGE BASELINE SPEEDS TO
AVERAGE SPEEDS DURING THE PROGRAM PERIOD, IN MILES PER HOUR

Site
SpeedLimit
Average Speed Baseline Period
Average SpeedProgram Period
Change
1
40
37.47
34.22
-9%
2
45
47.38
45.87
-3%
3
35
38.23
38.63
+1%
4
40
46.60
45.86
-2%
Average of All 4 Sites 42.42 41.15 -3%
Sum of Change Values -13%


CRASH DATA

MARION COUNTY CRASH RESULTS
Crash data were provided by the City of Indianapolis for the three special enforcement zones and three comparable locations that did not receive special aggressive driving enforcement effort. Data for each location were provided, by month for the program period, the same six-month period one year earlier, and for the intervening six-month period (i.e., an 18-month series beginning one year prior to program implementation). Data were entered in configured spreadsheets and included designations of crash severity (Fatal, Injury, and Property Damage Only/PDO) and primary collision factor (PCF). The following three figures, collectively labeled as Figure 6, illustrate the crash frequencies, presenting the numbers of injury and PDO crashes in each of the Marion County special enforcement zones during the program period in 2001 and in the same six-month period of the Year 2000; the shaded areas indicate the intervening six-month period.8

Figure 6. Crashes in the Marion County special enforcement zones.

Table 5 presents a summary of all crash data relevant to the Marion County aggressive driving program. The table shows that the three special enforcement zones and the three comparison zones experienced substantial increases in both injury and PDO crashes during the program period, compared to the same six-months of the previous year. The increases ranged from a six percent increase in injury crashes in the comparison zones to a 39 percent increase in PDO crashes in the special enforcement zones. Overall, crashes increased by 32 percent in the special enforcement zones and 24 percent in the comparison zones. The table also shows that the numbers of crashes for which a PCF associated with aggressive driving was cited increased by 21 percent in the comparison zones and by nearly twice that rate in the special enforcement zones.9

TABLE 5
SUMMARY OF ALL CRASH MEASURES DURING THE PROGRAM PERIOD AND THE SAME SIX-MONTH PERIOD ONE YEAR EARLIER: MARION COUNTY SPECIAL ENFORCEMENT AND COMPARISON ZONES

Measure
March-Aug. 2000
Comparison Period
March-Aug. 2001
Program Period
Percent
Change
Total PDO Crashes in Enforcement Zones
178
248
+39%
Total PDO Crashes in Comparison Zones
177
238
+34%
 
Total Injury Crashes in Enforcement Zones
81
95
+17%
Total Injury Crashes in Comparison Zones
103
109
+6%
 
Total Crashes in Enforcement Zones
259
343
+32%
Total Crashes in Comparison Zones
280
347
+24%
 
Total Target PCFs in Enforcement Zones
160
226
+41%
Total Target PCFs in Comparison Zones
196
238
+21%
 
Percent of Crashes w/ a Target PCF: Enforcement
62%
66%
+6%
Percent of Crashes w/ a Target PCF: Comparison
70%
69%
-1%


The substantial increases in the numbers of crashes in the comparison zones, and even greater increases in the special enforcement zones, suggest the influence of factors that were outside the control of the quasi-experiment. For example, a disproportionate number of rainy days or increased traffic volumes during the program period might be responsible for the increase in crash incidence; these issues will be discussed in a subsequent section of this report. However, calculating the proportions of all crashes with a primary collision factor associated with aggressive driving, for the program and comparison periods, largely eliminates the effects of uncontrolled variables that might influence the incidence of crashes; that is, in the current context, comparing the proportions of aggressive driving-related crashes is more meaningful than comparing the actual numbers of crashes. The results of these calculations, presented in Table 5, show that the proportions of all crashes in the enforcement zones that were associated with aggressive driving increased by about six percent. In contrast, the overall incidence of crashes in those zones increased by 32 percent. The proportions of all crashes in the comparison zones that were associated with aggressive driving remained the same, despite a 24 percent increase in crashes, overall, in the comparison zones.

TUCSON CRASH RESULTS
Crash data were provided by the City of Tucson for the four special enforcement zones and four comparable locations that did not receive special aggressive driving enforcement effort. Data for the special enforcement zones were provided by month for the program period, the same six-month period one year earlier, and for the intervening six-month period (i.e., an 18-month series beginning one year prior to program implementation). Crash data for the comparison zones were provided for the two six-month periods, rather than by month. Data were entered in configured spreadsheets and included designations of crash severity (Fatal, Injury, and Property Damage Only/PDO) and primary collision factor (PCF). The following four figures, collectively labeled as Figure 7, illustrate the crash frequencies, presenting the numbers of injury and PDO crashes in each of the Tucson special enforcement zones during the program period in 2001 and in the same six-month period of the Year 2000; as in the previous figures, the shaded areas indicate the intervening six-month period.

Figure 7. Crashes in the Tucson special enforcement zones.

Table 6 presents a summary of all crash data relevant to the Tucson aggressive driving program. The table shows that the four special enforcement zones and the four comparison zones experienced increases in PDO crashes and declines in injury crashes during the program period, compared to the same six-months of the previous year. The changes ranged from a 20 percent increase in PDO crashes in the enforcement zones to a 15 percent decrease in injury crashes in the comparison zones. Overall, crashes increased by 10 percent in the special enforcement zones and decreased by two percent in the comparison zones. The table also shows that the numbers of crashes for which a PCF associated with aggressive driving was cited decreased by three percent in the comparison zones and by nearly three times that rate in the special enforcement zones.


TABLE 6
SUMMARY OF ALL CRASH MEASURES DURING THE PROGRAM PERIOD AND THE SAME SIX-MONTH PERIOD ONE YEAR EARLIER: TUCSON SPECIAL ENFORCEMENT AND
COMPARISON ZONES

Measure
March-Aug. 2000
Comparison Period
March-Aug. 2001
Program Period
Percent
Change
Total PDO Crashes in Enforcement Zones
84
101
+20%
Total PDO Crashes in Comparison Zones
86
92
+7%
 
Total Injury Crashes in Enforcement Zones
61
59
-3%
Total Injury Crashes in Comparison Zones
62
53
-15%
 
Total Crashes in Enforcement Zones
145
160
+10%
Total Crashes in Comparison Zones
148
145
-2%
 
Total Target PCFs in Enforcement Zones
121
122
+1%
Total Target PCFs in Comparison Zones
104
98
-6%
 
Percent of Crashes w/ a Target PCF: Enforcement
83%
76%
-8%
Percent of Crashes w/ a Target PCF: Comparison
70%
68%
-3%


PROGRAM AWARENESS
The managers of both aggressive driving programs were encouraged to conduct surveys of public awareness to determine if local drivers received the programs’ public information and education messages. The Tucson Police Department did not conduct a survey; rather, the officers interpreted the response to their aggressive driver hotline as evidence of substantial public awareness. In contrast, the managers of the Marion County program commissioned Purdue University’s Center for the Advancement of Transportation Safety to conduct identical telephone surveys of 100 drivers each, prior to and at the conclusion of the Marion County Rub Out Aggressive Driving program. The Marion County pre- and post-program surveys contained 72 questions, the subjects of which ranged from demographic information to opinions about hypothetical changes to the Indiana vehicle code. Only two questions addressed public awareness of the aggressive driving program. The first of those questions asked, “Besides your experiences of aggressive driving while driving or as a passenger, what is your level of awareness of aggressive driving as a potential problem?” The responses to this question are presented in Table 7.

TABLE 7
RESPONSES TO THE MARION COUNTY PUBLIC AWARENESS SURVEY QUESTION #1

Response
Pre-Program
Post-Program
I read or hear about it on a daily basis.
15.1%
13.0%
I read or hear about it on a weekly basis.
32.6%
27.0%
I have read or heard about it at least once in the past month.
39.5%
33.0%
I have read or heard about it at least once in the past six months.
7.0%
15.0%
I have not read or heard anything about it until this interview.
5.8%
11.0%


The table shows that, overall, fewer drivers reported awareness of aggressive driving as a problem at the conclusion of the Marion County program than before it began. Fewer drivers reported hearing about the issue on a daily or weekly basis and within the past month, despite the extensive advertising campaign implemented by the Marion County Traffic Safety Partnership. Evidence that some drivers heard or read at least something about aggressive driving can be found in the 15 percent of respondents who reported hearing about the issue at least once during the past six months, up from seven percent prior to the program period. However, 11 percent reported that they had never heard or read anything about aggressive driving until the survey interview, compared to about six percent before the PI&E program.

The other relevant question on the survey asked about the primary sources of the respondents’ awareness of aggressive driving. Table 8 shows that television was the primary source of information both before and at the conclusion of the Marion County aggressive driving program. Awareness from newspapers showed the largest change, increasing as the primary source of information from 16 percent of respondents prior to the program to 31.5 percent at its conclusion. This increase probably reflects the Indianapolis Star’s substantial coverage of the program and of the fatal crash that resulted from a high-speed pursuit by an officer on special enforcement patrol.

TABLE 8
RESPONSES TO THE MARION COUNTY PUBLIC AWARENESS SURVEY QUESTION #2

Response
Pre-Program
Post-Program
Newspapers/magazines
16.0%
31.5%
Television
42.5%
47.2%
Radio
14.2%
4.5%
Other people
27.4%
14.6%
Other sources
0
2.2%

7 The special enforcement zone with the 40 mph speed limit declined by one percent, while one of the 35 mph zones declined by three percent and the other increased by one percent.

8 Corresponding figures for the Marion County Comparison Zones are included in Appendix B.

9 The Primary Collision Factors (PCFs) associated with aggressive driving are, Unsafe Speed, Failure to Yield Right-of-Way, Disregarded Signal/Sign, Left of Center, Improper Passing, Improper Turning, and Following Too Closely.