Hugh B. Borbidge, BSME, Director of Engineering Animations

Often, drivers involved in an accident will profess that each had their corresponding green light. Unless there is a signal malfunction, both cannot be right. Sometimes there are clues to help determine who was at fault.

In the following case, the tractor trailer driver stated that he had the green left turn arrow. The oncoming SUV driver stated that he had the green light and the witness said that they received the green light about 5 seconds after the accident happened.

Utilizing a signal timing plan, witness testimony, and the laws of physics, we can determine who was at fault. Working backwards, the witness statement puts the accident at 5 seconds prior to their light turning green. 5 seconds prior to the witness light turning green. The tractor-trailers light would have been a left yellow arrow. The tractor-trailers light would have been a left green arrow for 12 seconds prior to the left yellow arrow. It takes the tractor-trailer about 14 seconds to travel from the stop bar to the point of impact. These facts check out.

The 3D animation shows this signal timing along with the corresponding vehicle movements. It would not have been possible for the oncoming SUV to have had a green light under this signal timing pattern.

Hugh B. Borbidge, BSME, Director of Engineering Animations with DJS Associates, Inc., can be reached via email at experts@forensicDJS.com or via phone at 215-659-2010.

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