I realize now that the aggravation I felt was related to making sure I could pick up my son on time, and that the fear was about being trapped behind a slow and wobbly rider in traffic.

Riding at rush hour isn't a picnic, and going too slowly can make the bike harder to handle, which is unnerving when you're in a very narrow corridor. I think I'll practice going slowly this weekend...if I'm confident that I can handle the bike at 5-7 MPH then not being able to pass becomes more of a non-issue.