On Mon, 22 Sep 2008 01:15:57 -0700 (PDT)
David Martin  wrote:

> The term originally arose from those who would buy a season ticket
> rather than individual journey tickets as they could then commute
> their travel. Such people became known as commuters, and that term has
> spread to all who travel regularly to the same place of work.
> 
I'm doubtful of that explanation - the Latin commutare means to switch
or exchange (and is the root of English words such as commutator and
commutative) so it seems more likely to me that it simply refers to the
habitual switching between the locations of home and work.