Yeah, if the effect even matters, it wouldn't work well for short blocks.
Even for long blocks, you'd want to figure out that the light will be green for X seconds, which allows Y cars to get through, so only Y cars (and no more) would line up with the required spacing between them, and the ones behind that would pack in more tightly to save space. Then while the light is right, the next Y cars could get themselves into the correct configuration.
Even for long blocks, you'd want to figure out that the light will be green for X seconds, which allows Y cars to get through, so only Y cars (and no more) would line up with the required spacing between them, and the ones behind that would pack in more tightly to save space. Then while the light is right, the next Y cars could get themselves into the correct configuration.