3 buses, 1 car - that doesn't make for rush hour. Add in some skateboards and you'll have a ISU between classes.
I had a good friend in college who was from Sassenheim, which I just realized is very close to Leiden :)We are scheming to get back to the NL for longer than 5 days (though not exactly sure when that may happen), and if we do, we'd definitely hope to get out and see more than just Amsterdam. Maybe we'll have to head over to Leiden and Sassenheim :)
Bicycles are traffic too! ISU campus traffic is similar, yes, fewer cars than the outlying areas. Leiden is very compact and full of students.And close to Sassenheim! The best time to visit that area is tulip time, all the fields are between Sassenheim and Haarlem. It's really lovely. Let me know if you do plan a trip in the next year :)