In response to a blog thread I posted earlier this week regarding red light cameras,@Hank suggested changing signal timing in an effort to reduce incidents of red light running. His idea was to make the yellow lights last longer, then have overlapping reds, or all the signals red for a small period of time before the signals in one direction turn green. This is referred to in the engineering world as an ‘all red’ phase apparently.

I spoke to someone in the City’s Street Department who said that increasing amber lights doesn’t necessarily parallel increased safety. As they retime signals and implement photo red, they calculate the amber interval based on ITE Traffic Engineering Handbook Methodologies and that re-evaluations of clearance intervals resulted in decreased, not increased, yellow times.

An engineer for WSDOT Eastern Region that I talked to this morning said that the City of Spokane, and a couple other area jurisdictions, have taken a somewhat official stance on not using the ‘all red’ approach for a number of reasons. Apparently studies show that in communities with overlapping red lights, people adapt to this timing and either speed up to get through yellow lights or even go through red lights more often, as they subconsciously know they have a few extra seconds to get through the intersection before the signal from the other direction turns green. The all-red phase also impedes efficient traffic flow slightly by adding lag time between each light sequence. It’s only a second or three, but it’s repeated every time the light changes, hundreds of times daily.

The engineer I spoke with today said there are studies to that effect, but when I was digging around on the internet, all I could find were studies that say lengthening the yellow light and implementing an all red phase help cut down on red light runners to a small degree, but red light cameras were much more effective. I’ll continue to dig to see if I can find something more conclusive.

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