Traffic near the end of school

I'm fascinated by traffic and its causes. On my commute, I have a lot of time to consider how different things like different driving styles, road markings signs, and accidents affect traffic flow. I feel that I have a pretty comprehensive understanding of the various factors that affect the drive from Woodbridge, Virginia to McLean, Virginia during the morning and afternoon rush hours.

Of course, there are certain phenomenon that escape explanation. The one that is negatively affecting my commute right now is the end of the school year. What is it about the last few weeks of school that causes traffic to get so much worse? There doesn't seem to be anything about the last few weeks of school that explains the increased traffic, but it is certainly worse. My morning commute, which normally averages just under an hour, has jumped to averaging an hour and a half.

Normally, when dramatic traffic changes occur, there is a logical explanation. Take the beginning of school for example. A lot of people go on vacation during the summer and return right before school gets back in. So, it makes sense that traffic gets worse at that point. But, no one is returning from vacation right now. The busses are all driving the same routes. Nothings changed!

What do you think? Do any of my readers have any theories as to why this happens every year?