Wednesday, August 3, 2016

Green Light, Red Light Ratio

Today I received a very interesting question: Has there ever been a study on if the ratio of red lights to green lights that a driver encounters during a trip has an effect on the driver's mood? My response follows.

If the ratio green-to-red is 1:1 then this means that the driver has a 50% probability for either green or red as he or she drives down a street with a series of signalized intersections.  This is a poor ratio for a main arterial. A well managed arterial street should have at least a 7:3 green-to-red ratio; that is, many more greens than reds. This requires traffic signal optimization to accomplish.

Surprisingly, Honolulu is often the opposite, which makes it easy to fix, if anyone bothered to work on it. I demonstrated this to reporters in the two times I run for mayor. The best we could do was 1:1 which means the traffic lights operated at random!

As to the behavioral implications, I'm not aware of literature on past research associated with this ratio, but there is plenty of literature associated with congestion and loss of time. Of course one of the most irritating things is when one departs from a green, drives toward the next light which is green, but soon before s/he arrives at the intersection, the light turns red. This is terrible for loss of time, pollution, schedule failure for buses, etc.

The picture below shows the "bandwiths" of green light for both directions of a two way street.  Signal coordination is easy to do for one street, but it's complicated for a large city network, However, computers and software can optimize those with ease.