I’m amazed at the seasonality of traffic in the Kirkland/Redmond area on my commute. The summer was great, I could leave anywhere between 7 AM and 8:30 AM and expect very little traffic variability. But after Labor Day, the traffic snarled up again, as it had been before the start of summer. I read somewhere, that I can’t find at the moment, that this change is due to kids going back to school. It’s not that the kids themselves are driving at the same time, it’s that their parents are now driving them to school all at the same time.
One example on my commute is the backup along Juanita from the 98th Ave/116th Street intersection. On my drive down this morning, I passed the intersection at 7:15 AM with moderately heavy traffic, but no backup. On my return at 7:40 AM, traffic was backed up over 1.5 miles up the hill!
Morning commutes are fairly predicable, in my experience (today’s example was typical), and there’s a pretty clear cutoff for when traffic gets bad. Afternoon commutes, on the other hand, seem to have much greater variability, and span a much larger window. So, even if I leave early enough to avoid a morning mess, I still usually end up with some afternoon agony.