I saw this idea tried in North Miami FL many years ago and it was abandoned after a short trial period. What they discovered was that a normal driver looking at a green light would actually accelerate towards the intersection thinking that they could beat the "Clock" before it changed to red and the red light people thought that they could time the red light to get to the intersection at just the right moment when it turned to green. The results were disastrous! All drivers were actually never even considering to stop and either accelerated or only slowed down so that when they go to the intersection no one was prepared to stop. The intersection was littered with bumper and head light parts and it was abandoned after only a few days.