The “Oh Crap” Moment

Justin P. Schorr, Ph.D., Principal Collision Reconstruction Engineer
Animation by Hugh Borbidge, BSME, Director of Engineering Animations


In collision reconstruction, the “oh crap” moment is the location, in both space and time, which represents a vehicle operator’s final opportunity to perceive, react, and avoid a hazard. Initially, you may think this is the same as the time required to perceive, react, and stop your vehicle – however, it is a bit more intricate than that. Identification of the “oh crap” moment requires an understanding of the time-space continuum and, while this may seem complicated, you don’t need to be Sheldon Cooper to understand.
In the accompanying animation we have an “observer” (the approaching vehicle) and a “hazard” (the pedestrian). We start by calculating how much distance is required for the observer to perceive, react, and stop based on:

  • The speed of the observer and the type of vehicle (often passenger vehicle or heavy truck)
  • A typical perception plus reaction time (often 1.5 seconds during the day and 2.0 seconds a night)
  • A typical coefficient of friction for the roadway (often 0.7 for a passenger vehicle on a dry roadway)

Now we know the location where a collision goes from avoidable to imminent. From here, the next step is to determine how long the hazard needs to be visible in order for the observer to have sufficient time and distance to perceive, react, and avoid it. We make this determination by calculating the time it would take the observer to travel from this distance without performing any evasive action (stopping, slowing, swerving, etc.). If the hazard is visible for longer than this time – then the laws of physics establish that the observer has not yet arrived at their “oh crap” moment. Bazinga!
Justin P. Schorr, Ph.D., Principal Collision Reconstruction Engineer and Hugh Borbidge, BSME, Director of Engineering Animations with DJS Associates, Inc., can be reached via email at or via phone at 215-659-2010.

Waymo Technology Safer than Human Drivers?

Autonomous Vehicles

Justin P. Schorr, Ph.D., Principal Collision Reconstruction Engineer
Waymo internally develops, funds, conducts, publishes, and peer-reviews its own internal study which shockingly reaffirms their long and deeply held belief that their technology is safer than human drivers.
Waymo, LLC. published a March 8, 2021 paper titled Waymo Simulated Driving Behavior in Reconstructed Fatal Crashes within an Autonomous Vehicle Operating Domain.  The paper was authored by six employees of Waymo, LLC.  As a company, Waymo has boasted about their safety record for years and, more recently, has been developing creative ways to showcase what they believe to be dominance of their self-driving systems over us humans.
The paper is pointless.  The study is designed such that achievement of the expected outcome was obvious and inevitable.  Briefly, the study collected police data for 117 fatal collisions occurring over a 10-year period in Arizona.  Admittedly, limited data was available to reconstruct the details of how these collisions occurred.  Of these 117 collisions, only 72 were included in the data set used for analysis.  Researchers identified 91 “vehicle actors” in the 72 collisions – 52 initiators and 39 responders (initiators being when the assumed actions of a human driver initiated the collision sequence and responders being the assumed actions, or inactions, of a human driver in responding to the actions of an initiator).  The human driver was then “replaced” with the Waymo self-driving technology in a simulation framework and the scenario was “re-run” with the tech in control.  The outcomes were recorded and voila Waymo proved their technology is better than human drivers! Continue reading “Waymo Technology Safer than Human Drivers?”

Stop Sign Obstruction: Was it the Cause of a Motorcycle Collision?


Justin P. Schorr, Ph.D., Principal Collision Reconstruction Engineer
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 “Stop Sign Obstruction: Was it the Cause of a Motorcycle Collision?”

Heads-Up Displays: Aiding or Obstructing?


Laurence R. Penn, Senior Forensic Animation / Video Specialist
Justin P. Schorr, Ph.D., Principal Collision Reconstruction Engineer
The CES annual tradeshow (organized by the Consumer Technology Association) has been touted as the most influential tech event in the world – the place where revolutionary consumer technology is announced and displayed to the public. Since the first show took place in 1967, many products that seem old or nostalgic to us now were considered the highest of high-tech at the time when they were first announced. Such products included VCRs (1970), CDs (1981), HDTVs (1998), and drones (2015).
At the most recent CES show, which occurred virtually mid-January 2021, the newest technologies included vehicle heads-up displays or HUDs. With advances in miniaturizing and optimizing real-time 3D LIDAR scanning, their presence in new vehicles is becoming more and more prevalent. Combining real-time object collision detection and digital display technology, data can be displayed on dashboards or windshield to make drivers more aware of their surroundings or provide entertainment while the vehicle is in self-driving autonomous mode. In the demo videos of this new technology, “on-screen” alerts as well as visual cues are aligned with the actual position of a potential obstacle or hazard. Continue reading “Heads-Up Displays: Aiding or Obstructing?”

CNN Interviewed Dr. Justin P Schorr, Principal Reconstruction Engineer, Regarding the Information Your Vehicle Knows About You

Infotainment Expert Witness

Cars increasingly resemble a smartphone on wheels, storing personal information such as our location, how we drive, who we talk to and how to reach them. Some even hold a way to join our home WiFi network. If you’ve ever sold an old smartphone or laptop, you probably thought to wipe the hard drive first, to protect your privacy. When we sell a car, or return a rental car, a similar thought may not cross our minds, but cybersecurity experts say it should.
This month a security researcher described buying old Tesla infotainment systems online and finding personal information such as the home addresses and WiFi passwords of the previous owners. The news was first reported by InsideEvs. Searches of eBay reveal that infotainment systems from brands such as BMW, Ford, Cadillac and Mercedes-Benz are currently available for sale.
“This isn’t just a Tesla thing, it’s every single infotainment system,” said Justin Schorr, president of DJS Associates, a vehicle forensics firm that reconstructs crashes using on-board data. “Think of all the vehicles with screens, this is ubiquitous almost.”
Read the full article here.

Reconstruction of Multi-Vehicle Collisions


Justin P. Schorr, Ph.D., Principal Collision Reconstruction / Transportation Engineer
Multi-vehicle collisions, sometimes involving dozens of vehicles, typically occur during periods of adverse weather conditions such as snow, ice, and/or fog (some may recall the recent 20+ vehicle collision in Pennsylvania). When these collisions occur on high-speed, limited-access highways, there can be severe consequences as a result of the multiple impacts (at the time of this writing it has been reported that there were 2 fatalities and over 35 people sent to the hospital as a result of the aforementioned pile-up in Pennsylvania). However, from a reconstruction standpoint, with so many vehicles involved, how does one define the dynamics of the collision? Continue reading “Reconstruction of Multi-Vehicle Collisions”

The Reconstruction of a Legend

Justin and Steve

Justin P. Schorr, Ph.D., President, Principal Collision Reconstruction / Transportation Engineer
There are three parts to every collision: the vehicle, the roadway, and the driver. In honor of my father – and following the conceptual writing prompt he loved the most (“let’s see how far we can stretch this analogy”) – this article will take a look at the “great collision of life” and see how our framework applies. Yes, I could use this space, which we are grateful to have been awarded, to gloat about the recent “cease and desist” letter sent to Tesla (which I have been calling for the past 2 years), or to rewrite the ABC’s of the latest trend in crash reconstruction (another one of my father’s favorites). It may not be conventional – but there is no way I am going to pass up the opportunity to gloat about my father to such a distinguished audience.
The Vehicle. My old man was a machine. The vehicle which he drove on a daily basis was 5 foot 10 and 160 pounds – and this was true from the time he was in graduate school until the day he passed away. He used to tell me that he was under 5 feet tall when he graduated high school and then grew 8 inches between high school and college. I held out hope that the same would happen to me, but unfortunately, I am still waiting for 5’8” to turn into anything taller than 5’8”! Not only did his last moments come just after he dismounted his spin bike – but I will always remember the neon yellow runner’s pullover he had been wearing earlier that day. Dad was an athlete. Scratch that, he couldn’t hit a golf ball over 200 yards, and he had the worst wrist shot and slap shot I’ve ever seen. Dad loved to exercise. Much better. At 61 years old, his aerobic endurance was miles beyond my 33-year-old “vehicle,” and he had even completed a marathon (he had run a few) in under 4 hours. Continue reading “The Reconstruction of a Legend”

A U-Turn Dispute: Can it be Resolved with Limited Data?

U Turn Collision

Justin P. Schorr, Ph.D., Principal Collision / Reconstruction Engineer, President of DJS Associates, Inc.
Heading northbound on a sunny day, a stone mason operating a super duty “work” type truck went to execute a U-turn at a signal-controlled intersection. There were no sight distance limitations and no signs indicating that U-turns were prohibited. He testified that while turning from the left northbound travel lane, he was “rear-ended” by a Toyota passenger vehicle, which was also in the left lane, behind him. Simple rear-end collision… right? [Stealing a line from my father which he stole from Paul Harvey and subsequently beat into the ground] “And now for the rest of the story.”
The dispute is as follows:
While the Toyota operator agreed that she was in the left lane and that the truck was making a U-turn – her claim was that the truck began its turn from the adjacent lane (immediately to her right) and then turned across the left lane, cutting her off. In addition to no measurements being recorded at the scene and the absence of any witnesses, by the time the case reached litigation neither vehicle was available for inspection. However, several photographs were taken which showed damage to the vehicles and the point of rest position of the truck. Through the use of the vehicle specifications along with the damage photographs, to-scale three-dimensional computer models of each vehicle was created which accurately reflected the damage profiles shown in the photographs. Continue reading “A U-Turn Dispute: Can it be Resolved with Limited Data?”