Who Was the Driver?

Collision Reconstruction Engineer

Robert T. Lynch, PE, Principal Collision Reconstruction Engineer
Case Synopsis: Four buddies went out drinking one night. While on their way home from the bar their vehicle departed the roadway to the right, as it was negotiating a left curve. The Event Data Recorder (EDR) in the vehicle indicated that the vehicle was traveling above the speed limit, at a speed above the critical speed for the curve, which resulted in the roadway departure and subsequent counterclockwise yaw before a frontal impact with a tree. All four occupants were unbelted, and three of the four occupants were ejected from the vehicle. Two of the ejected occupants were fatal. The one occupant that remained in the vehicle was the owner of the vehicle. The State Police conducted a criminal investigation to determine who was driving, concluding that it was the owner of the vehicle, the one who was not ejected. Continue reading “Who Was the Driver?”

Lug Nut Damage Analysis

Lug Nut Expert Witness

Robert T. Lynch, P.E., Principal Collision Reconstruction Engineer
Often in lane change collisions involving commercial vehicles on a highway, the exposed lug nuts from a steer tire on the commercial vehicle will create obvious damage to the door(s) of a passenger vehicle, with little to no damage to the truck itself. The lug nuts will dig into the side of the vehicle and create a circular swirl pattern from the rotating wheel which is imprinted onto the doors and/or panels while the vehicles are in contact with each other. Continue reading “Lug Nut Damage Analysis”

Thinking Outside the ‘Box’ for Pedestrian Safety


Robert T. Lynch, PE, Principal Collision Reconstruction Engineer
Vehicle manufacturers market their advanced safety features to keep occupants safe, but what about the safety of those who are outside the vehicle?
Advanced driver assisted technologies such as pedestrian detection systems and automatic emergency braking are designed to help mitigate pedestrian collisions or eliminate them altogether. But these systems are limited in their ability to actually detect pedestrians, especially at night.
Over the past decade, pedestrian fatalities have increased by approximately 50% at night (and 15% during the day).
Current systems rely on cameras and radar to determine if there is something in front of the vehicle. In low-light environments, the cameras, like our eyes, struggle and radar systems have a high degree of false positives and false negatives to pass as being consistently reliable.
To improve upon the current systems, lidar sensors can be installed on vehicles to map the environment in real-time, and then software can predict the paths of both the pedestrian and the vehicle. If a collision course is imminent, automatic emergency braking will intervene. Lidar sensors have a clear benefit to camera-based systems because they are not sensitive to light and work equally well at night as in the day. However, installing lidar sensors in vehicles is still cost-prohibitive. As manufacturers continue to push the limits of partial automation, lidar systems are expected to become more and more prevalent in vehicles. Perhaps then we will see a significant decrease in pedestrian impacts at night.
Robert T. Lynch, PE, Principal Collision Reconstruction Engineer with DJS Associates, Inc., can be reached via email at experts@forensicDJS.com or via phone at 215-659-2010.

Perception-Reaction Time

Reaction Time

Robert T. Lynch, PE, Principal Collision Reconstruction Engineer
A colleague recently sent me a link to an online game to test one’s reaction time (see link below). The game simulates a (right-hand drive) vehicle traveling down a straight, hilly roadway with trees, signs, and deer to the sides of the roadway. When the player sees a red stop sign with a hand on it, they are to click the mouse or press any key on the keyboard to stop the simulation. Reaction time, the time between when the stop sign is presented on the screen and when the mouse or keyboard is clicked/pressed, is then compared to how 2,000 people above the age of 18 performed in this same simulation. Continue reading “Perception-Reaction Time”

To Deploy or Not to Deploy – That is the Dilemma

Airbag Deploy

Robert T. Lynch, P.E., Principal Collision Reconstruction Engineer
The purpose of an airbag in a vehicle is to offer an increased level of protection to occupants in a crash. To be able to do this the airbag needs to deploy in crashes where added protection is needed, but not to deploy in crashes when the risk to the occupant would outweigh the benefit. Generally frontal airbags will deploy if the Delta-V, or change in velocity of the vehicle, exceeds 8-14 miles-per-hour (MPH). However, there are scenarios when airbags have deployed in collisions where the Delta-V was less than 8 MPH, or airbags did not deploy in collisions where the Delta-V was above 14 MPH. In these latter instances, a claim for failure to deploy is often made by an injured party. Continue reading “To Deploy or Not to Deploy – That is the Dilemma”

3 Vehicle In-Line Collision: Who Hit Whom?

Robert T. Lynch, P.E., Principal Collision Reconstruction Engineer
Whether it’s the result of sudden slowing of traffic on a limited access highway or the vehicles queued up at a red light, multiple vehicle in-line collisions are a common occurrence. In-line collisions are among the easiest to reconstruct for severity, but the question of who hit who, or more precisely the order of impact(s), is not as easy to establish, and is sometimes indeterminable.
For example, say vehicle 1 (V1) is behind vehicle 2 (V2) who is behind vehicle 3 (V3). It is often quite clear from the vehicle damage that the front of V1 hit the back of V2, and the front of V2 hit the back of V3; however, the driver of V1 often claims that V2 hit V3 before V1 hit V2, whereas the driver of V2 claims that they were struck in the rear by V1, resulting in V2 then being pushed into the rear of V3. Continue reading “3 Vehicle In-Line Collision: Who Hit Whom?”

Crush Analysis


Robert T. Lynch, P.E., Principal Collision Reconstruction Engineer
Since 2013, for most vehicles equipped with event data recorders (EDR) that record 5 seconds of pre-crash speed, performing a crush analysis to figure out vehicle speeds has become increasingly unnecessary for performing a reconstruction. However, there are instances where a crush analysis is still warranted. For example, the vehicles involved may be older and/or do not have an EDR; the vehicles involved may have been repaired with key airbag system components replaced (EDR is typically a function of the Airbag Control Module (ACM)); or the vehicles involved may have been salvaged/scrapped/crushed and are no longer available for data extraction. Continue reading “Crush Analysis”

October is National Pedestrian Safety Month


Robert T. Lynch, P.E., Principal Collision Reconstruction Engineer
Three out of every four pedestrian fatalities occur at night. This fall, as the days get shorter and the nights get longer, the risks for pedestrians increase. This year, NHTSA has launched the first National Pedestrian Safety Month with the goal of increasing awareness about pedestrian safety, reminding both drivers and pedestrians that staying safe is a shared responsibility. Continue reading “October is National Pedestrian Safety Month”

Reconstruction of a Vehicle-Bicycle Collision

Robert T. Lynch, P.E., Principal Collision Reconstruction Engineer
A doctor would frequently ride his bicycle from his home to the train station as part of his commute to work. One morning before sunrise, the doctor was riding along on a sidewalk before he crossed a six-lane roadway where he was struck by a vehicle after nearly crossing all six lanes of traffic.
Surveillance video was provided from a nearby business that captured the pre-impact movements of both the bicyclist and the vehicle. However, this video did not capture the actual point of impact, as the camera was located too far away (over 500 feet), and several trees were obstructing the clear line of sight. Also, the ambient illumination was still dark, effecting the clarity of the video.
DJS was asked to use the provided surveillance videos to reconstruct the incident to the greatest extent that it could be reconstructed. The roadway was documented with high-definition surveying (HDS) laser scans, drone aerial images and video, and terrestrial photographs and video, with specific focus on documenting the environment in the vicinity of the surveillance cameras. Using this data, an accurate, to-scale, three-dimensional model of the environment was created. The surveillance video was then camera-matched to the environment. The movements of both the bicyclist and vehicle were tracked through the environment and pre-impact speeds were able to be determined. Continue reading “Reconstruction of a Vehicle-Bicycle Collision”