Synching can work, but I think a lot of it depends on how the underlying street network is laid out. In NYC the lights on the avenues are synched, but the benefit really only goes one way - basically, if you're going downtown you can "surf" the lights as they turn yellow/red in the direction of traffic flow. However, because of the cross-streets, the uptown lights can't flow the same way, so you get much more of a stop-start effect.