Coming out of San Francisco every Friday....anywhere from 3:00pm to 5:30pm adds at least 20 mins to as much as another full hour to an already long commute. And I'm sure it's like this in other metropolotin areas. But my question is why. What exactly is the cause of this? And why do people try to go home early on Friday's if they know damn well they might as well wait 'till later to avoid almost doubling their commute time?