[legion]

The main road in Bloomington (Veterans Parkway--coincidentally the busiest road south of the Chicago area in the state seeing 50,000 cars a day) is like that. Further, the lights are timed so that the busy side gets the green arrow last. (In the morning, most traffic is south-bound and the south-bound left turn lane gets the green arrow last--the opposite is true in the evening.) I can tell you the effect. The speed limit is 45 mph and the effective speed during rush hour is 25-35 mph--all because of the poor light timing.

I think it is a scheme to limit traffic flow...like speed bumps or round-abouts.