Conflicting Crash Testimony - Expert Reconstruction Expert Article

In this case, a Honda collided head-on with a BMW. In the course of litigation, each driver provided a substantially different version of how the collision occurred. Robson Forensic was retained to conduct reconstructions based on each driver’s description and determine which version was more consistent with the physical evidence.

Conflicting Crash Testimony - Expert Reconstruction

A Honda heading eastbound on a highway with two lanes in each direction, plus a central turn lane, collided head-on with a BMW attempting to exit a driveway and head westbound. In the course of litigation, each driver provided a substantially different version of how the collision occurred. Robson Forensic was retained to conduct reconstructions based on each driver’s description and determine which version was more consistent with the physical evidence: the damage to both cars and their final resting positions. The case resolved by settlement.

RECONSTRUCTION

The scene photos show:

• The BMW perpendicular to the south curb, with its front wheels up the curb, and to the east of the driveway.
• The Honda parallel to the north curb and in the westbound lanes.

The damage to the cars and their final rest positions were then used in a collision reconstruction to determine which scenario (BMW Driver or Honda Driver) best fit the physical evidence.

Computer reconstructions were performed for both scenarios using PC Crash1[1], a computerized crash reconstruction program, which utilizes the principles of Conservation of Energy and Conservation of Momentum.

• The results of these reconstructions are shown in the following two Figures, labeled BMW Driver Scenario and Honda Driver Scenario. Both scenarios were reconstructed based on the following:
• The angle at maximum engagement of the two vehicles was based on the V imprint in the front of the BMW.
• The right front wheel of the Honda was entrapped by damage.
• The remaining wheels of the Honda were free to rotate.
• All the wheels of the BMW were free to rotate.

SCENARIOS

Honda Driver Scenario

For the Honda Driver Scenario, the location of the vehicles at impact was based on the BMW making a turn directly into the left westbound lane. BMW’s speed of 18 mph at impact was based on accelerating rapidly from a stop in the driveway, to correspond with the driver of the Honda’s description of the BMW “blasting out” of the driveway. The Honda’s speed at impact was based on the Honda Driver’s estimate of 35 mph.

The Honda Driver Scenario is not consistent with the final rest position of both vehicles. The speeds and resulting momenta of the two vehicles offset each other, both vehicles stop near impact, and impact is further to the east than the Honda’s final rest position.

BMW Driver Scenario

For the BMW Driver’s Scenario, the location of the vehicles at impact was based on the Honda’s final rest position and the BMW being fully in the center lane at impact. The BMW’s speed was assumed to be zero, and the Honda’s speed 50 mph at impact, based on the BMW driver’s testimony. The front wheels of the BMW were turned slightly to the right, as seen in the photos.

The BMW Driver’s Scenario is a better fit to the final rest positions. The Honda stops close to its final rest position. The BMW is directed towards its final rest position. Not accounted for in the computer reconstruction is the crown of the road. The BMW would roll down the crown and up onto the curb. The location of the vehicles at impact is sufficiently remote from the driveway to be consistent with the BMW turning into the westbound lanes in two moves, as described by the Driver of the BMW: first into the center lane and second into the moving westbound lanes.

FINDINGS

Based on the information available, subject to change with new information, and to a reasonable degree of professional certainty, our expert concluded the following:

1. There is no cross shear on the front of the Honda, as would be expected if the BMW was moving at impact.
2. The reconstruction better fits the BMW driver’s description of how the collision occurred than the Honda driver’s.

SOURCES

1[1] PC-Crash, Version 6.2 (2001). See SAE Paper 960885: Validation of PC-Crash—A Momentum-Based Accident Reconstruction Program.

Featured Expert

Peter J. Leiss, P.E., C.F.E.I., C.V.F.I.

Automotive Engineer & Crash Expert

PJ is an expert in vehicle engineering and crash reconstruction. He commonly investigates and testifies in matters pertaining to vehicle crashworthiness, vehicle performance/handling dynamics, and… read more.