Many areas of accident investigation can lead to erroneous assumptions and improper applications of engineering fundamentals. Below is an example of an accident recently reported in a local newspaper.  The basic facts of the accident are as reported; however, the names and details have been changed.

This accident was of particular interest to us. Two weeks prior, Craig Sellers, president of Professional Investigative Engineers, had a similar experience while exiting at the same off-ramp. Fortunately, Craig recognized the problem early. He flashed his car's headlights and swerved slightly trying to get the other driver's attention. The driver looked at Craig like he was insane; however, when the driver reached the interstate, he stopped and safely turned around.

In hindsight, Craig felt he should have reported his experience to the highway patrol. Following the accident described below, the highway department added additional signs to warn unsuspecting drivers.

Accident Reported in Newspaper

I-404 off-ramp crash injures five

Mountain County, February 23: Five people were injured - three seriously - in a head-on collision on the I-404 eastbound off-ramp at Mountain Village. An out-of-state BMW accelerating up the off-ramp in the wrong direction struck a Volvo exiting the interstate and proceeding down the off-ramp at approximately 65 mph, according to the local police report. "The impact speed of the accident was 120-plus mph," said an officer with the Mountain Village Police Department. "It's a wonder nobody died."

The statement that "the impact speed was 120-plus mph" is clearly misleading and may deceive those involved in the post-accident analysis. The closing, or approach, speed of the accident may have been approximately 120 mph, but the damage incurred during an accident reflects only motion of the vehicles relative to each other and not with respect to the road. Hence, if we are asked to determine the speed of vehicles involved in a collision and are provided only photographs of the damage incurred to each vehicle, our job is impossible. To provide the information requested, an accident reconstructionist must know details of the accident site, including location of first contact, location where the vehicles came to rest, the physical properties of the roadway and any skid marks that may have been created.

Another misconception is that the damage incurred to a vehicle during an accident is directly proportional to its speed prior to impact. Many have argued that the faster vehicle of two involved in a collision will sustain the greatest damage; others have argued the opposite. The correct answer to this problem is that the strongest vehicle will incur the least damage, and the weakest vehicle will incur the greatest damage. This is true whether the strongest vehicle is moving and the weakest vehicle is stopped, the weakest vehicle is moving and the strongest is stopped, or both vehicles are moving.

Determining vehicle speed prior to a collision is thus dependent on many factors. But before we present too much information and spoil all the fun, let us present our contest scenario and questions.

Scenario: Two identical vehicles are traveling in opposite directions on a level surface. Both vehicles are going 65 mph and strike one another directly head-on. The vehicles contact such that the impact is distributed equally to both vehicles.

Published by Professional Investigative Engineers. If you have questions or comments, contact Craig Sellers at csellers@callpie.com or 1.866.552.5246.