I used to have a short enough commute that if anything went too wrong I could walk my bike home in a half hour or less.
I just moved in with my mother for the summer to save some money before moving out west for school and now my commute is about 115km (72mi) round trip which usually takes me less than two hours each way (but has taken me 2.5 hours on windy days).
I carry a cell phone and although I haven't had to use it yet, I have called a couple of times after work when I wasn't feeling up to par and asked for a ride home. The journey is about an hour by car so it doesn't really save me any time.