Your route sounds like an even better candidate for a bicycle
commute.

Yes, if you live in the south. Bikes only work about half the year
here in northern PA.

What causes them to cease functioning the other half of the year?

If you meant "it's too cold to ride", consider about twice as many people
regularily commute by bicycle in PA than in GA...

http://www.kenkifer.com/bikepages/survey/commuter.htm