&gt; the first real question to be asked really is, why does everyone need to commute to the same place in the same time?<p>Schools (K-12) are one of the biggest drivers of why at the same time.  Schools start and end at specific times.  This (usually) requires one adult to be around to drop them off and pick them up at school or the bus stop, especially K to at least early middle school. Because of this a lot of people in (sub)urban areas leave from home and from work around the same time.  The difference in traffic congestion is drastic when you compare summer to the school year in larger cities with no meaningful mass transit.