Longer Yellow Lights = Shorter Green Lights?

May 31, 2008

Recently it was suggested in the local newspaper that adding additional time to yellow lights will cause the green light cycle to be shorter:

Bernie Hillermann, committee member, asked Wagner to look at extending the length of the yellow lights at the intersection. “Four seconds is not long enough,” he said.

Wagner said the duration of the lights is based on various factors, including the size of the intersection. The timing and duration of signals are set by engineers to optimize the movement of traffic through an intersection, she explained.

Increasing the duration of the yellow light would take time away from the green light, which means fewer vehicles could get through the intersection on the green light, she noted. “That’s part of the problem,” Stratman remarked. “Everyone thinks they are a traffic engineer. They think they know the solution.”

Is it a “problem” when pillars of the community, such as Mr. Hillermann, makes a reasonable suggestion regarding lengthening the duration of yellow lights? And to the casual observer, it sounds rather elitist chunking verbal barbs at intelligent people for simply making rational suggestions.

Probably it wasn’t intentional, but the quote taken from Mrs. Wagner left the idea with many readers, that you lose green when you add yellow.

You can add a second to a yellow light and keep the green light timed at the original length. Fact. Where you do lose green is in total cycles. Say there are 1000 green, yellow, red cycles in a 12 hour period. Because you took more yellow may result in fewer cycles, maybe 950 instead of the original 1000. All of which would be transparent to the driver and have virtually zero input on through-put rates – or how many cars can pass through a given restriction (such as an intersection).

So, yes, technically Judy is correct in saying we lose green. We do not, however, lose green in a specific cycle, and to suggest so is misleading.

But ultimately, even this argument is without merit because we are told that Red Light Cameras and lite timing is about safety. I think very few would argue that adding yellow does not increase safety at an intersection. My contention is born out by the fact that over 80% of red light infractions occur less than one second into a red light.

So if we trade a second of green for a second of yellow, isn’t it worth it if it saves a single families lives? Of course it is.

What is more, why are almost all lights in our city timed at the same 3.9 seconds that our 2 red light camera intersections are timed at, where approach speeds are considerably higher? Take a look at Jefferson and 5th – the approach is 30 mph and we have a…..3.9 second yellow – exactly the same for 100 and 47 that is over twice as wide and has a speed limit of 45 mph. Yes, some pretty high level science is going in to determining our yellow light sequences.

Guy W. Midkiff

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Published in: on May 30, 2008 at 11:47 pm  Leave a Comment  

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