Motorcycle Collision: “I Didn’t See the Stop Sign!”

Steven M. Schorr, PE, President of DJS Associates ::::
Synopsis: A motorcycle was traveling southbound on a two-lane, two-direction roadway approaching a T-type intersection with a four-lane roadway. The motorcycle operator (plaintiff) failed to stop at the posted stop sign, and entered the four-lane roadway where he was involved in a collision with a westbound vehicle.
The motorcycle operator testified he was traveling at the posted speed limit of 35 mph as he approached the intersection; but, due to the stop sign being obstructed, perceived the traffic control at the last instant and did not have sufficient time and distance to stop prior to entering the four-lane roadway.
The plaintiff contended that tree branches obstructed the stop sign and therefore sued the State [the governing authority for the roadway], as well as the owner of the property on which the tree was located. The area of the collision was reportedly changed by the time suit was filed. The plaintiff provided no specific “hard copy” data, including photographs or measurements, to establish the obstruction or the extent of the obstruction. Continue reading “Motorcycle Collision: “I Didn’t See the Stop Sign!””

What Direction Was the Vehicle Traveling – An Analysis of an Intersectional Collision

Steven M. Schorr, PE, President, DJS Associates, Lead Collision Reconstruction Engineer ::::
A collision occurred, at a stop controlled intersection, between the front of a motorcycle and the driver (left) side of a passenger vehicle. The police took photographs of the point of rest of the vehicles and of the damage to the vehicles. Simple enough, right? Well, not so fast. When the police interviewed the involved parties, the operator of the passenger vehicle said she was northbound on the two lane, two direction roadway and was turning left to head westbound onto a one-way street when the northbound motorcycle, traveling in the same direction she was traveling, came up on her left side in the opposite lane trying to pass her. The motorcycle struck her driver side door as she was turning. The motorcycle operator informed the police that he was indeed northbound; however, as he approached the intersection, the passenger vehicle entered the intersection from his right, traveling westbound on the one-way street. As the passenger vehicle entered the intersection, it “cut him off” resulting in his motorcycle contacting the driver side of the passenger vehicle. Continue reading “What Direction Was the Vehicle Traveling – An Analysis of an Intersectional Collision”

Who Was the Driver?

Who Was the Driver?

Steven M. Schorr, PE, President of DJS Associates, Inc., Lead Collision Reconstruction Engineer ::::
It is a dark, stormy night… a vehicle attempts to travel around a left curve but unfortunately leaves the travel surface to the right, moves off the roadway, into the woods and the front of the vehicle strikes a tree. As the vehicle rebounds off the tree rotating and rolling over, both front seat occupants are ejected before the vehicle comes to rest on its roof.
Event data from the vehicle indicates that the vehicle was traveling 70 miles per hour around a curve marked with a curve warning sign and a 25 mile per hour speed advisory sign. Both occupants are killed. The question… who was the driver?
The engineering analysis of this case begins in the same manner as all reconstruction cases… with the physical evidence.
Continue reading “Who Was the Driver?”

LIDAR: Just What Is It?


Steven M. Schorr, PE, Collision Reconstruction Engineer ::::
Did You Know that… LIDAR stands for Light Detection And Ranging.
It is defined as “A remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances) to the Earth. These light pulses—combined with other data recorded by the airborne system— generate precise, three-dimensional information about the shape of the Earth and its surface characteristics.”
LIDAR is the foundation of HDS Laser Scanning which provides engineers and others the opportunity to create accurate three-dimensional environments for use in analyses. Continue reading “LIDAR: Just What Is It?”

Watch Where You Stand

Off-Tracking of Right Turning Tractor-Trailer

Steven M. Schorr, P.E., President of DJS Associates ::::
A tractor-trailer operator was executing a right-hand turn at a four-way intersection in a major city. As he was completing his turn and heading straight down the roadway onto which he turned, he was flagged down by a person who advised him that his truck contacted a pedestrian.
The physical evidence indicated that indeed the right side of his trailer did contact the pedestrian and knocked him down whereupon the pedestrian was run over by the right rear trailer tires of the right-turning tractor-trailer.
These dynamics are consistent with the properties of a right (or left) turning tractor-trailer wherein the tractor pulls the trailer. The trailer itself has no steering therefore as a result, in a right-hand turn, the right rear tires of the trailer will always track to the inside of the path of the right front tires of the tractor. This concept is referred to as “off-tracking”. The longer the trailer, the further to the inside (of the front tractor tires) the rear trailer tires will “off-track”. Continue reading “Watch Where You Stand”

Video Reveals What Really Happened with Tractor-Trailer / Pedestrian Accident

Truck Pedestrian Accident

Steven M. Schorr, P.E., President of DJS Associates ::::
Increasingly, the data available to review as part of a collision reconstruction includes video, sometimes obtained from nearby surveillance cameras, and sometimes acquired from the vehicles themselves.
Many commercial vehicles are equipped with event data recorders in the form of a camera that captures different views as the vehicle proceeds along. Depending on the equipment, the data is either recorded continuously, or the camera is manually activated by the operator, or recording is activated by a defined sudden deceleration threshold.
Recently, we were provided with a video from a truck which showed a passenger vehicle on the right shoulder with its flashers on and its hood up. The daytime video showed a pedestrian suddenly emerge from behind the raised hood of the vehicle on the shoulder, and moved directly into the path of the approaching truck. The pedestrian was struck by the right front/center of the truck. Although the conclusion as to how the collision occurred seemed obvious, we were tasked with evaluating the event from a collision reconstruction perspective, i.e., what were the factors that led to this event and, in this case, were there any additional causal factors other than the actions of the pedestrian. Continue reading “Video Reveals What Really Happened with Tractor-Trailer / Pedestrian Accident”

Provide the Data – Even if YOU Don’t Think it is Important

Car Accident

Steven M. Schorr, President of DJS Associates ::::
The case involved a passenger vehicle which moved off a two-lane, one-way, limited access roadway to the left into the center grass median and into the guide rail. During the collision event, the passenger vehicle was overrun, from behind, by a straight body truck resulting in a fatality in the passenger vehicle.
The engineers for side A were provided police scene images of the site and vehicles. After an inspection of the site (the vehicles were not made available), a preliminary reconstruction of the vehicle dynamics was completed by engineers A by photogrammetrically locating, to scale, the physical evidence noted in the scene images and using that data as a foundation for the engineering analysis.
Continue reading “Provide the Data – Even if YOU Don’t Think it is Important”

Typical Issues in Railroad Grade Crossing Collisions

Railroad Crossing

Steven M. Schorr, PE, President of DJS Associates, Inc. ::::

1. Roadway 2. Vehicle 3. Driver – these are the three factors in all collisions.
With a collision involving a non-gated (i.e. use of passive traffic controls such as signs and lane striping) railroad grade crossing, the vehicles typically involved include a passenger car or truck and a train which cannot steer and takes longer to stop than passenger vehicles. As a result, grade crossings need to provide the passenger vehicle operator, and the train operator, sufficient data in order to properly and safely approach and cross over the intersection between the roadway and railroad tracks. With regard to the train, just like a roadway, the approaching tracks have a speed limit for the train.
Continue reading “Typical Issues in Railroad Grade Crossing Collisions”

Collision Reconstruction 101: Physical Evidence, Physical Evidence, Physical Evidence!

Physical Evidence

Steven M. Schorr, PE, Collision Reconstruction Engineer ::::
The foundation of any collision reconstruction is the application of the laws of physics to physical evidence left as a result of the collision. This is done in an effort to determine, if possible, how the collision occurred. The laws of physics do not change. As such, the variable in every reconstruction is the available physical evidence. It is that data which determines to what extent a vehicular collision can be reconstructed.
When teaching young engineers about how to properly reconstruct the collision, the mantra is always “always default to the physical evidence.” That is, when attempting to reconstruct a collision the first three items (pieces of physical evidence) one should look for include the:
Continue reading “Collision Reconstruction 101: Physical Evidence, Physical Evidence, Physical Evidence!”