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Ray Helmer - Civil Engineering Expert

Traffic Signal Accident: Both Claim Green Light

By: Ray Helmer
Tel: 713-777-7611
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Many vehicular accidents happen because drivers are in too much of a hurry or they are distracted by any number of things. They just are not paying close enough attention to their surroundings. Traffic accidents at signalized intersections are common where both drivers claim the other driver is at fault. Both insist they had the green light, and both really believe it. Some drivers may not be fully familiar with traffic laws and the meaning of certain traffic signal indications. The traffic accident which is described below shows how such a situation might occur.

Unit 1, a commercial vehicle consisting of a Freightliner truck tractor pulling a flatbed trailer approached the intersection from the west. The driver pulled his vehicle into the left turn lane, in order to make a left turn to proceed north.

Unit 2, a pickup truck, approached the intersection from the east. The driver stated that he was traveling 42 mph in a 45 mph speed zone. He further stated that he was traveling in the inner lane of the two-lane westbound roadway and that it was raining, so he had his windshield wipers and lights on. When he saw Unit 1 turning left across his traffic lane, he braked, his vehicle went out of control and he struck the flatbed trailer.

The driver of Unit 2 stated in his deposition that the color of his traffic signal was green. Therefore, the traffic light controlling Unit 1's left-turning movement would have been in the "Permissive Only" mode, consisting of a circular green ball, but not a "Protected Only" mode, which would have displayed a green arrow for vehicles intending to make a left turn.

In the "Permissive Only" mode, vehicles may make left turns only after yielding to oncoming traffic and pedestrians. This is indicated on the "Left Turn Yield on Green" sign that was in place to the upper right of the traffic signal that controls left turns from eastbound to northbound, which is the traffic movement that Unit 1 made.

Apparently the driver of Unit 1 misinterpreted the "Left Turn Yield on Green" sign and believed that he could turn left when the circular green ball was displayed (rather than the green arrow) and that other traffic would yield to him. This would explain why he turned left in front of Unit 2, thereby causing the traffic accident.

Mr. Helmer obtained the Traffic Signal Timing Diagram from the State Department of Transportation, because the traffic signal was at an intersection on a State Route. His review of the Timing Diagram and geometrics of the intersection proved that the above statements about the various traffic movements were true.

The case was settled favorably for Mr. Helmer's client, who was the Plaintiff (driver of Unit 2), on the basis of Mr. Helmer's review of documents and Expert Report.


Mr. Ray G. Helmer has been a Licensed Professional Engineer in several states for more than 50 years. He has extensive experience in engineering design of streets, highways, and specifically traffic signals. He has participated in approximately 300 Expert Witness cases for both plaintiff and defense attorneys. He is available for traffic engineering investigations, expert reports, depositions and trial testimony.

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