Paying Attention: Will an Alert Driver Avoid a Crash?


Robert T. Lynch, PE, Senior Collision Reconstruction Engineer ::::
Possibly… but not necessarily. I recently visited the Miami, Florida area on vacation and encountered several of these signs on the highways in and around the city. The wording of the sign had me reflecting on my undergraduate logic class, literally learning about the P’s and Q’s of modus ponens (if P then Q) and modus tollens (if not Q then not P). By the rules of inference, if a statement is true, then so is its contra-positive. In other words, (if P then Q) is the same as (if not Q then not P).
Now that we all are up to speed with our P’s and Q’s, when the Miami sign is applied to the logic framework, the sign would read: if a driver is alert then a crash can be avoided. Accepting this statement as true indicates that its contra-positive is also true: if a collision occurs then the driver was not alert. While this statement makes logical sense, as drivers who are not paying attention are more susceptible to crash, not all collisions occur due to driver inattention. Continue reading “Paying Attention: Will an Alert Driver Avoid a Crash?”

Collision Reconstruction – A Desktop Analysis Approach

Robert T. Lynch, PE, Senior Collision Reconstruction Engineer ::::
Some cases don’t reach our desk until months or even years after the incident and the physical evidence that is created immediately after the collision is, at times, long gone. Any potential roadway evidence such as tire marks or gouge marks may have vanished, or the road has been repaved and the vehicles may have been repaired, or totaled, and sent to a salvage yard without a trace.
For these instances, vehicle and/or site inspections may not be feasible, or they would not be expected to provide any data that would be substantial to the reconstruction. That is, an inspection of a repaired vehicle would not be as useful as photographs displaying the damage from the collision, and although an inspection of a resurfaced site would provide roadway widths and other measurements, no roadway evidence would be expected to remain after such a long period of time. Continue reading “Collision Reconstruction – A Desktop Analysis Approach”

Sunglare … Where?


James R. Schmidt, Jr., BSME, Sr. Collision Reconstruction Engineer ::::
This is one of the times of year where motorists are regularly encountering sun glare. The sun is low in the eastern sky during morning rush hour. The sun is low in the western sky during evening rush hour.
Take this morning, for example. I was on my ride to work, and voila … sun glare! Continue reading “Sunglare … Where?”

Watch For Motorcycles… And Riders Watch The Road

Robert T. Lynch, PE, Sr. Collision Reconstruction Engineer ::::
This spring we have experienced some unseasonably warm weather, already breaking 80 degrees a couple days during the month of April here in the Philadelphia area. If you’re anything like me, owner of a motorcycle and a pulse, you’ve been itching for warmer weather for the past 4 months in order to reacquaint your bike to the curves of your favorite back roads.
But before you grab your gear, kick the tires, and saddle up, just take a moment to recall how different, and mentally taxing, it can be to ride a motorcycle, specifically how to handle turns on a motorcycle as opposed to a vehicle. A motorcycle is leaned left or right to turn and not steered, which reduces traction potentially creating a slippery situation. Traveling around a curve with loose gravel in the roadway is one of the biggest hazards that a rider will face over the next month or so as the remnants of salt, sand and loose gravel deposited on the roadway during the winter season still remain. Continue reading “Watch For Motorcycles… And Riders Watch The Road”

Amish Horse and Buggy

James R. Schmidt, Jr., BSME, Sr. Collision Reconstruction Engineer ::::
During my travels this past holiday season, I encountered a single-horse Amish buggy heading eastbound on State Route 372 between Buck and Quarryville, in Lancaster County, PA. These buggies are a familiar sight in this area of Lancaster County. A couple of years ago during the height of summer, we counted over 30 buggies during our one-way travel along this route!
As a collision reconstruction engineer, I’m always interested in how fast vehicles are travelling, among other parameters. So, I’d like to take this opportunity to report a “fun fact”. Once again, using my Garmin dash cam and the GPS speed displayed thereon (note that I forgot to turn off the daylight savings time setting, as it’s dark outside by nearly 6 PM!), I am reporting the average speed of a typical single-horse Amish buggy on generally flat, level ground to be on the order of 6 mph. Specifically, the dash cam reported my speed as 6 mph as I followed the buggy for a short distance, while waiting for opposing traffic to pass and then ultimately for the buggy to make its left turn. Also, by measuring the distance between the two positions shown below on an aerial photograph (157 feet) and dividing by the time to travel this distance (18 seconds), I have independently confirmed my speed, and hence the buggy speed, to have been 6 mph on average.


While a “fun fact” to those reading, this point of reference for a horse and buggy speed could come into play in a future evaluation, as DJS Associates has been retained on several Amish buggy crashes over the years.
James R. Schmidt, Jr., is a Sr. Collision Reconstruction Engineer with DJS Associates and can be reached via email at or via phone at 215-659-2010.

Not all “Black Boxes” are Created Equal, Until Now…

Black Boxes

Robert T. Lynch, PE, Sr. Collision Reconstruction Engineer ::::
Nearly all vehicles sold in the US since 2013 have an event data recorder (EDR), more commonly known as a black box, which is capable of recording data in non-trivial crashes. A non-trivial crash, as defined by 49 CFR Part 563 – Event Data Recorders, is any collision resulting in a change in velocity (Delta-V) to the vehicle of more than 5 miles per hour over 150 milliseconds. Older vehicles with EDRs would typically only record data in frontal collisions, but the current regulation for vehicles requires EDRs in newer vehicles to record data in front, side and rear impacts greater than 5 miles per hour Delta-V.
If a vehicle is compliant with Part 563 (vehicles 2013 and newer) and is involved in a crash resulting in a Delta-V above 5 miles per hour, 5 seconds of pre-impact speed, acceleration and braking data will be recorded in the EDR. While this information is often valuable to reconstruct the collision, the absence of data stored in the EDR can be equally as beneficial to the reconstruction.
Continue reading “Not all “Black Boxes” are Created Equal, Until Now…”