Steven M. Schorr, PE ::::
Case Synopsis: A pedestrian on the east side [southeast corner] of a city street was looking to the north, waiting for the traffic signal to direct pedestrians to cross. A northbound tractor-trailer was executing a right turn to head eastbound. The tractor passed the pedestrian, but the pedestrian was knocked down by the right side of the trailer and then run over by the right rear trailer tires. The pedestrian was moved prior to the police documenting the area. There was a photograph of the point of rest position of the tractor-trailer which had finished its turn prior to being “flagged down” by witnesses who observed the collision. The witnesses gave contradictory testimony as to whether the pedestrian was on the curb or in the street at the time of the collision.
Expert Analysis: The point of rest position of the tractor-trailer was defined using the police photograph. This was a key piece of evidence in the analysis. Utilizing the specifications of the tractor-trailer and “physics-based” computer software, the specific path of the tractor and trailer [including the “off-tracking” of the trailer] was modeled. The analysis showed that in order for the tractor-trailer to be in the orientation it was in at its point of rest and as defined by the police photograph, the right side tires of the trailer had to have crossed onto the southeast sidewalk as the vehicle executed its right turn.
Result: It was this “off-tracking” path [common to articulated vehicles where the tractor is essentially dragging the trailer behind it] that resulted in the right rear tires of the trailer mounting the curb, and striking the pedestrian who was located properly on the southeast corner sidewalk.