[dmazin]

Some cities in America have traffic-synchronized streets where a driver going a certain (indicated all along the street) speed should hit the greens every time. The problem one one street I've seen it used for is, the sign is very vague about when this system is active "during peak traffic hours" so I do not know when to go the suggested speed or not.

[ojilles]

Pretty common elsewhere in the world too. In the Netherlands they call it the "Green Wave", and marketed as such. I suspect b/c speeding in those area's really doesn't buy you anything. So when traffic is light, they double as a "speed bump" :-)

[eru]

Common in Germany as well.