Rush hour

One of the chief threats to SBB's punctuality is the sheer density of traffic on busy lines like Killwangen-Altstetten.

The morning rush hour, which starts at about 6:30, used to run until 8:30, with the peak starting at 7:30. The morning rush has now extends to 9:00. The evening rush hour runs from 16:30 to 21:00, with the peak continuing to 20:00 now that more businesses are open later.

The evening peak is more difficult than the morning because the network must also handle freight trains that collect cars from customers and deliver them to the classification yards. By the time the morning rush begins, the freight trains that distribute cars sorted during the night in the yards have mostly already run (they start at about 4:00 in the morning.).

Weeks when school is in session generally see more train delays because more people are in the S-Bahn, and because pupils tend to hold the doors for each other.