Red Light Cameras & Yellow Light Lengths


Recently I was invited to testify at a red light camera hearing, by State Senator Jim Lembke (R) of St. Louis, sponsor of Senate Bill 211,  which would ban the use of Red Light Camera’s in Missouri.

Link to SB 211:

Unfortunately the bill died in committee, receiving only two votes. To describe my experience testifying as frustrating, is an understatement. I was given 2 minutes to lay out a case against red light cameras – which is impossible considering the complexities of the issue.

I simply asked the committee how Red Light Cameras prevent accidents at intersections? To know this answer, one most know why drivers plow through intersections and how sensitive this behavior is to external stimulus such as the threat of a red light camera ticket.

What “independent” research shows time and time again is that the vast majority of drivers that run red lights are distracted, for a myriad of reasons, and show no sensitivity to a camera. For the very small minority that intentionally run red lights, very few result in accidents because of “all way” red light sequencing. This gives opposing drivers an added degree of safety in the event a red light is ran.

To the credit of red light camera operators, this small subset of offenders, is sensitive to red light cameras. But again, these drivers, by and large, are not causing the horrific T-bone type accidents.

This brings me back to the conversation of yellow light sequence timing. All of our HW 100 intersections have yellow light sequence lengths of exactly 4.01 seconds – regardless of the approach speeds. And on HW 100 we have 45 mph and 55 mph opposing intersections.

This is problematic. Simply put, a car traveling 45 mph is traveling at 66 feet per second. Applying a standard co-efficient of friction (.7), a constant deceleration rate of 15 feet per second can be derived. What that means is that your average 4,000 pound car will take about 4.1 seconds  to decelerate to a complete stop.

But the problem, which is already obvious, gets worse. It takes the brain of an average person about 1 second to recognize the change from green to yellow and about another second for the brain to send a signal to the foot to begin braking.

In the best of situations, our yellow light should be set at 6.1 seconds for the 45 mph approach, certainly not the current 4.01 seconds.

The situation is even worse for the approach to Jefferson, on HW 100, from the west. This speed is 55 mph and is poorly marked, with no speed signs all the way back to the Washington West Elementary School intersection.

This fact alone, already causes apprehension and indecision on the part of the driver. The deceleration rate for 55 mph, is about 5.5 seconds, with an additional 2 seconds for recognition and response. This suggests a 7.5 second yellow light as opposed to the current 4.01. second yellow light.

Part of the problem is a complete lack of light length standards on the part of MoDot. I have brought this point up with MoDot management, in the past, and nothing has been done about it. MoDot determines light sequence lengths – not the City of Washington. I believe this to be an unsafe situation for roads and should be addressed immediately before someone is seriously injured.

And btw, these numbers can change by as much as 40% for an 80,000 pound tractor trailer, an elderly driver, or adverse driving conditions.

Now, try explaining this to a transportation committee in 2 minutes or less. And most regrettably, I didn’t have a chance to give the proper recognition to the gentlemen in the $4000 Armani Suits, seated behind me, from the red light camera companies.

Source Documents:
Vehicle Stopping Distance And Time
Longer Yellow Lights reduce accidents

Guy W. Midkiff
Ward III, Councilman
Washington, Mo.

Published in: on February 26, 2009 at 11:57 pm  Leave a Comment  

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