On Mon, 22 Sep 2008, Rob Morley wrote:

> 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.

OED sayeth:

commute, v.
     b. absol. spec. To purchase and use a commutation-ticket. Also, more 
generally, to travel daily or regularly to and from one's place of work in 
a city (by any means of conveyance); also transf. and fig. orig. U.S.

1889 Cent. Dict., Commuter, one who commutes. 1906 Daily Chron. 25 Feb. 4 
There are many business men who practically divide their time between New 
York and Chicago, and commute (the American term for taking season 
tickets).

commutation
     9. attrib. and Comb., [...] commutation ticket (U.S.), a ticket issued 
by a railway company, etc., at a reduced rate, entitling the holder to 
travel over a given route a certain number of times or during a certain 
period; a season-ticket.

1848 Amer. Railroad Jrnl. 29 July 481/3 Commutation tickets.., costing $5, 
are issued at Trenton, signed by B. Fish, which entitles the receiver to 
eight passages between Trenton and New Brunswick, by any line on the 
route. 1885 Good Words July 450/1 A single Commutation ticket is given, 
numbered and dated on the day on which it was issued.

Webster's dictionary of 1913 has to say:

Commutation ticket. A ticket for transportation at a reduced rate in 
consideration of some special circumstance, as increase of travel; 
specif., a ticket for a certain number of, or for daily, trips between 
neighboring places at a reduced rate, such as are commonly used by those 
doing business in a city and living in a suburb. Commutation tickets are 
excepted from the prohibition against special rates contained in the 
Interstate Commerce Act of Feb. 4, 1887 (24 Stat. 379), and in 145 U. S. 
263 it was held that party tickets were also excepted as being "obviously 
within the commuting principle."

And WordNet:

     * S: (n) commutation ticket, season ticket (a ticket good for several 
trips or to attend a season of entertainments; sold at a reduced rate)

So it seems that the term 'commuter' definitely does come from a kind of 
ticket. Why those tickets are called that is not entirely clear to me, but 
it does look more likely that it's to do with their being at a reduced 
rate than associated with going back and forth between two places. It's 
'commute' in the sense of 'his sentence was commuted to life in prison', 
rather than 'what's purple and commutes?' [1].

tom

[1] An Abelian grape.

-- 
Also, a 'dark future where there is only war!' ... have you seen the
news lately? -- applez