THE RELATIVE FREQUENCY OF UNSAFE DRIVING ACTS IN SERIOUS TRAFFIC CRASHES

SUMMARY OF IMPORTANT FINDINGS

This study was conducted to determine the specific driver behaviors and unsafe driving acts (UDAs) that lead to crashes, and the situational, driver and vehicle characteristics associated with these behaviors. A sample of 723 crashes involving 1284 drivers was investigated at four different sites in the country during the period from April 1, 1996 through April 30, 1997. The crashes were selected using the National Automotive Sampling System (NASS) protocol and provided a fair sample of serious crashes involving passenger vehicles in the United States. In-depth data were collected and evaluated on the condition of the vehicles, the crash scene, roadway conditions, driver behaviors and situational factors at the time of the crash. Investigators used an 11 step process to evaluate the crash, determine the primary cause of each crash, and uncover contributing factors.

• Crash causes were attributed to either driver behavior or other causes. In 717 of the 723 crashes investigated (99%), a driver behavioral error caused or contributed to the crash. Of the 1284 drivers involved in these crashes, 732 drivers (57%) contributed in some way to the cause of their crashes. There were six causal factors associated with driver behaviors that occurred at relatively high frequencies for these drivers and accounted for most of the problem behaviors. They were:

• DRIVER INATTENTION 22.7%
• VEHICLE SPEED 18.7%
• ALCOHOL IMPAIRMENT 18.2%
• PERCEPTUAL ERRORS (e.g. looked, but didn't see) 15.1%
• DECISION ERRORS (e.g. turned with obstructed view) 10.1%
• INCAPACITATION (e.g. fell asleep) 6.4%

Problem types in terms of crash configuration and specific behavioral errors were also identified. The following seven crash problem types, when associated with specific behavioral errors, accounted for almost half of the crashes studied where there was a driver behavioral error:

• SAME DIRECTION, REAR END

• TURN, MERGE, PATH ENCROACHMENT

• SINGLE DRIVER, ROADSIDE DEPARTURE

• INTERSECTING PATHS, STRAIGHT PATHS

• SAME TRAFFIC-WAY, OPPOSITE DIRECTION

• BACKING, OTHER, MISCELLANEOUS, ETC.

Countermeasures were identified and recommended in the following areas in order to deal with these driver behaviors and unsafe driving acts:

• EDUCATION & TRAINING – for driver inattention factors, gap acceptance

• LAW ENFORCEMENT – to reduce excessive speed, following too closely, and driving while impaired

• TECHNOLOGY BASED REAR END CRASH AVOIDANCE SYSTEMS – in development as part of the Intelligent Transportation Systems (ITS) initiative to compensate for driver inattention and following too closely

• TECHNOLOGY BASED INTERSECTION COLLISION AVOIDANCE SYSTEMS – part of ITS to compensate for driver errors at intersections

• TECHNOLOGY BASED LANE KEEPING SYSTEMS – part of ITS to prevent lane encroachment and roadside departure crashes

There were certain limitations to the data. While the sample was reasonably representative of serious crashes involving passenger cars that occurred in this country during that time period, the 723 crashes were not nationally representative because they were selected from only 4 of 24 NASS sites. Also, while the inter-rater reliability for many of the causal assessments was as high as one can expect for studies of this kind, the determination of causal factors still relied upon investigator judgment and clinical assessment.

This study confirms other research showing that driver inattention, driver impairment, unsafe vehicle speeds, and driver fatigue are important factors in serious crashes. It also provides unique insight into driver information failures and unsafe driving acts that lead to crashes under certain specified conditions.