Two Collision Contributors, One Code Violator


Robert T. Lynch, PE, Senior Collision Reconstruction Engineer ::::
A motorcycle traveled across the double yellow centerline into the opposite travel lane on a rural, two-lane roadway in order to pass a farm tractor. When the tractor turned left at the intersection a collision occurred. DJS Associates was retained to evaluate the matter to determine the contributing factors that led to the subject incident. The incident would have clearly been avoided if the tractor operator hadn’t turned left or if the motorcyclist decided not to pass the tractor at the intersection. So, in general, the actions of both operators could be considered as contributory. However, a review of the (Pennsylvania) state statutes indicated that the actions of the motorcyclist were in violation of the vehicle code while the tractor operator’s actions were in compliance with the vehicle code
The vehicle code requires that a left-hand turn be completed from the left-most lane available, and that the driver of a vehicle intending to turn left at an intersection yield the right-of-way to any vehicle approaching from the opposite direction which is so close as to constitute a hazard. From an engineering perspective, the actions of the tractor operator to turn left at the intersection from the travel lane were in compliance with the vehicle code. Continue reading “Two Collision Contributors, One Code Violator”

Evaluating Motorcycle Skid Marks

Motorcycle Accident Reconstruction

Robert T. Lynch, PE, Senior Collision Reconstruction Engineer ::::
When a motorcycle leaves a skid mark leading up to a collision, it is indicative of hard braking applied by the rider prior to impact. The skid mark can be from either a locked front or rear tire, or both, as the rear tire follows the same path as the front, laying one skid mark on top of the other. It is not always obvious from the skid mark deposited on the roadway whether both wheels are locked or only one wheel was locked to create the skid mark. An evaluation of the motorcycle tires could potentially determine if both or only one tire was locked. For instances, where there is evidence of only the rear wheel being locked to create the skid mark, one must not assume that only the rear brake was applied. This assumption leads to a reduced roadway friction coefficient, and subsequently, an artificially low speed of the motorcycle.
Even though the evidence may only indicate that the rear wheel was locked during the pre-impact phase of the collision, the absence of a front tire skid mark does not preclude the possibility that the front wheel was also braked, just not enough to lock the wheel to leave a skid mark. As a rider myself, I know that a locked front wheel is something to avoid, but a locked rear wheel is okay as long as the motorcycle is upright, and traveling along a straight path. The Pennsylvania Motorcycle Operator’s Manual states, “If the front wheel locks, release the front brake immediately then reapply it firmly.” The front brake lever should be squeezed firmly and progressively as the front brake can provide 70% or more of the potential stopping power. Continue reading “Evaluating Motorcycle Skid Marks”