Hi home2mars –
I don’t know how to add weight to the comments from a couple of experts.. The best analogy is the city subway or city bus system. Get your ticket and hop one. If you miss one, catch the next one. Indeed, there are trains in Switzerland that do not permit or require reservations.
Apart from the special scenic trains, you will find reserved seats on Intra-Europe trains that pass through Switzerland on the way to or from another country.
I would like to confirm that you mean Zürich Main Station, and not Zürich Airport ( Flughafen). D0 you? Are you hauling luggage?
If by some chance you meant the airport, there are about 4 connections per hour, but the only one that does not require a change of trains at – for example, Zürich main station – is the one at 0915.
1960man has noted the times (xxo4 and xx35) for the direct trains form Zürich main station to Luzern. There is also one at xx10 which requires a change at Rotkreuz. It is not a big station, so change there is not difficult.
I suspect that you have learned about the SBB timetable,
and other information at this site:
http://www.sbb.ch/en/
but, the tips and tricks on this page are useful:
http://www.myswissalps.com/ti metable
If you check the trains in the SBB timetable, you will usually see in the information for each journey not only the duration, but the occupancy rate.
For your education, look up a train to Zürich, for example, from Luzern, on a weekday at around o830. You’ll probably see some red symbols for high occupancy. Going the other way (to Luzern) during rush hour does not show that problem.
Slowpoke