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Number 243                                                                                                   April 2001


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

DRIVER INATTENTION IS A MAJOR FACTOR IN SERIOUS TRAFFIC CRASHES

The National Highway Traffic Safety Administration (NHTSA) conducts a sampling of all traffic crashes in America with the National Automotive Sampling System (NASS). NHTSA commissioned a study by Veridian Engineering, Inc. to examine crashes in the NASS to determine the specific driver behaviors that led to crashes and the situational characteristics of both drivers and vehicles associated with these behaviors. A short technical report and a detailed technical report are now available.

A sample of 723 crashes involving 1,284 drivers was investigated at four NASS data collection sites (Allegheny County, Pennsylvania; Knox County, Tennessee; Jefferson and Gilpin Counties, Colorado; and Seattle, Washington) from April 1, 1996 through April 30, 1997. These sites were selected because they had high scene and vehicle inspection rates and very high interview completion rates. The research team interviewed drivers and occupants involved in crashes. They also reviewed the police crash report and examined the physical evidence generated by the crash. While the physical evidence pattern normally is sufficient to verify specific statements, on occasion the lack of a distinctive pattern can require another approach. Discrepancies were resolved from the preponderance of evidence.

Using all the available data, the researchers assigned a crash type and identified pre-existing conditions (such driver, roadway, vehicle, and environment) that may have contributed to the crash and the critical event that precipitated the crash occurrence. The critical event can be an action (a pedestrian darted into roadway, for example) or it can be a point in time (the driver entered the curve without reducing travel speed).

Next, the researchers evaluated the specific reason(s) for the occurrence of this crash and the contributions of driver behavior, and environmental, roadway, and vehicle conditions. A single crash cause can have a number of contributing factors. For example, a causal factor, such as lost directional control on a wet surface, might have factors that include the wet road surface, the driver traveling too fast for existing conditions, and the presence of bald tires on the vehicle. For those cases where driver behavior was the primary causal factor, or a contributing factor, the specific behavior was assessed as to whether or not an unsafe driving action was involved.

Finally, each crash was evaluated as to whether or not the unsafe driving action was due primarily to an element of the vehicle or environment that the driver was unaware of and could not have anticipated (for example, a speed reduction sign had fallen down, or the tail lights of the car ahead had failed) and whether the driver was aware of an increased crash risk of the particular driving actions. Drivers were asked if they could have driven differently to prevent the crash and if they thought they were taking a chance in the way they were driving. The researchers determined whether the cause of the unsafe driving action was inattention, perception, decision-making, motor skills, other, or unknown.

Causal Factors

Causal assessments were completed for 1,239 (96.5 percent) of the drivers in the sample. Of the 1,284 drivers contained in the sample, 507 (40.3 percent) did not contribute to crash causation. The relative frequency of the unsafe driving actions were computed on the 59.7 percent of the drivers who had been identified as contributing to the crash. The table below shows the relative frequency of the most dominant causal factors.

HOW TO ORDER

For a copy of The Relative Frequency of Unsafe Driving Acts in Serious Traffic Crashes, Short Technical Report (28 pages) or the Final Report, The Relative Frequency of Unsafe Driving Acts in Serious Crashes (85 pages plus appendices), write to the Office of Research and Traffic Records, NHTSA, NTS-31, 400 Seventh Street, S.W., Washington, DC 20590 or fax (202) 366-7096. Paul J. Tremont, Ph.D., was the contract manager.

Causal Category
Assignment Level

Percentage of Drivers Contributing to Causation

Driver Inattention Primary (Sole Factor)

Primary (in Combination)

Contributory

Total

16.7

5.2

0.8

22.7

Vehicle Speed Primary (Sole Factor)

Primary (in Combination)

Contributory

Total

6.8

3.8

8.1

18.7

Alcohol Impairment Primary (Sole Factor)

Primary (in Combination)

Contributory

Total

6.0

11.1

1.1

18.2

Perceptual Errors

(Looked, did not see)



(Accepted Inadequate gap)

Primary (Sole Factor)

Primary (in Combination)

Contributory

Primary (Sole Factor)

Total

8.9

0.1

0.1

6.0

15.1

Decision Errors

(Turn/cross with obstructed view)

(Violated red signal)

(Attempted to beat phasing signal)

(Violated stop sign)



Primary (Sole Factor)

Primary (Sole Factor)

Primary (Sole Factor)

Primary (Sole Factor)

Total



4.7

2.6

2.1

0.7

10.1

Incapacitation

(Fell asleep)

(Seizure, blackout)



Primary (Sole Factor)

Primary (Sole Factor)

Total



4.4

2.0

6.4

U.S. Department of Transportation
National Highway Traffic Safety Administration
400 Seventh Street, S.W. NTS-31
Washington, DC 20590

Traffic Tech is a publication to disseminate information about traffic safety programs, including evaluations, innovative programs, and new publications. Feel free to copy it as you wish.

If you would like to receive a copy contact:

Linda Cosgrove, Ph.D., Editor, Evaluation Staff
Traffic Safety Programs
(202) 366-2759, fax (202) 366-7096
E-MAIL: lcosgrove@nhtsa.dot.gov

U.S. Department of Transportation National Highway Traffic Safety Administration
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