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Abstract
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In 1987, following implementation of the Washington state safety restraint mandatory usage law, collision statistics indicated an increase in motor vehicle crashes where occupants had died while utilizing safety restraints. In order to investigate this issue, a "Fatal Collision Research Team" was established to evaluate and reconstruct collisions where a restrained occupant had died. Collisions were analyzed over a three year period and included 337 crashes involving 1058 occupants of which 446 died.
The team analyzed fatal collisions involving restrained occupants, and documented restraint usage and survivability of the crash. Crash survivability was determined by the Collision Deformation Classification (CDC) which measures the extent of crush or intrusion into the passenger occupant area of the vehicle. The extent of intrusion that would result in survivable or non-survivable collisions was defined separately for front, side, rear, and rollover crashes. The survivability of the crash was determined individually for each occupant and independently of whether the occupant lived or died. In addition, a measure of deceleration forces (Delta V) was used when appropriate for the type of crash and when sufficient data were available.
The major findings were: (1) that in the majority of cases where a restrained occupant died, the fatality can be attributed to the extent of vehicle crush and deceleration forces, i.e., the crash forces and dynamics made the crash non-survivable, and (2) restraint misuse seemed not to be a major contributory factor in fatal crash injuries.
Following enactment of the 1986 Mandatory Seat Belt Usage Law in Washington, vehicle crash statistics showed a marked increase in fatalities to occupants who were using safety restraints. During the years 1987 to 1990 there were 599 fatalities to restrained occupants out of 2,255 total occupant fatals (26.6%) as compared to 191 out of 1,960 (9.7%) for the years 1982 to 1985. In addition, seat belt use increased from an estimated 20 percent to an observed use rate of 55 percent during 1989.
Very few hypotheses were offered as explanations for this increase in fatalities to belted occupants other than attributing it to an increase in belt use. Opponents of the belt use law contended that the increase in deaths to restrained occupants reflected a lack of protective benefits of seat belts while others suggested that mis-use of belts was the major contributing factor.
The Washington Traffic Safety Commission undertook a project to investigate this issue. A Fatal Collision Research Team was formed to evaluate, and when appropriate, reconstruct crashes in which an occupant died while wearing a safety restraint. The team's objective was to determine crash dynamics, forces, and vehicle deformation in order to assess whether the crash was survivable or not regardless of seat belt use.
Team members were selected for their training and experience in major crash reconstruction, and included representatives from local and state police, the National Transportation Safety Board, and a retired police accident reconstructionist as program manager. In addition, the Chief Medical Examiner for the King County Medical Examiner's Office provided consultation in injury analysis |