There are many things to take into account. I heard a story about Silicon Valley. There is a major highway linking all of the cities that people use to get to work. There are feeder roads from the residential areas to this major highway. The lights on the feeder roads are intentionally unsynchronized to reduce the traffic flow. This is to act as a storage area on the feeder roads so that the entry of cars onto the major highway is kept down. There seems to be a maximum injection rate. If cars arrive at the major highway in too large a volume they cannot get into the traffic flow on the major highway as quickly and stack up at the entry point and block the cross streets.