From: tssmith@netcom.com (Tim Smith)
Subject: Re: ? about engine sets
Organization: Netcom Online Communications Services (408-241-9760 login: guest)
Distribution: usa
Date: Sat, 23 Jan 1993 14:19:36 GMT

In article <1jp1qtINN4as@grapevine.EBay.Sun.COM> maral@repare.EBay.Sun.COM writes:
> My son asked me a question the other day and I couldn't answer him
> so I thought I would tap the knowledge of all you experts.  The
> question is why do trains utilize various engine types when pulling
> a string of cars and why do some point forwards and some backwards?
> I kind of would like to know myself.  A 10 year old and 36 year old kid
> appreciates your response.

Sounds like you're a newcomer here.  Welcome, and I'll try to keep
the answers simple.  There are three things going on:

First, as you noted, most freight (and some passenger) trains are
pulled by more than one engine.  Out west, it's not uncommon to see
five or more engines at the head of a train, and sometimes several
more pushing at the end, or pushing and pulling in the middle.  All the
locos (units) are usually controlled from the front cab.

Second, locomotives, unlike automobiles, run just as well in reverse
as in forward.  This is true of steam and electric locomotives as
well as diesels.  The thing that determines the natural direction of
travel is the location of the engineer's cab.  Most diesel
locomotives have the cab up front.  Some older electric locomotives
had a central cab, and these could run "naturally" in either
direction.

The third thing is that when a locomotive, or a set of locomotives,
gets to the end of the run, or to some "division point" in the run, it
then usually goes back the other way on a different train.  So if you
have, say, two diesels coupled back end to back end, it's very simple
to uncouple them from the train they were pulling, switch them onto a
parallel track, and couple them to a new train.  Now the back becomes
the front, and the new crew uses the former back cab.  But if you had
to turn the engines around, you'd need a lot of extra track (a loop
or a "Y"), requiring more real estate and more complicated switching
operations.

Another example of railroads' saving time and space are the so-called
"push-pull" commuter trains.  These have a single diesel locomotive
at the front of the train, usually facing out of the main city
station, and a cab built into the end of the last car of the train. 
When the train gets to the end of its "outbound" run, the engineer
can just go back to the cab in the last car, and run the train back
into the city by controlling the locomotive remotely from there.  The
locomotive is now running in reverse, pushing the train.

As far as different types of locomotives on a train, this is less
common.  (Don't be misled by the color or marking of the
locomotives.  It's common now for railroads to use "pooled" power, so
you might see, say, a bright yellow Union Pacific unit in the middle
of some blue Conrail units, pulling a train somewhere east of
Chicago--not UP territory.)  But a railroad can mix locomotives with
some freedom, when needed.  An extreme example is what you find on
many excursions of old steam locomotives.  Railroads don't like
considering the possibility that their line could be tied up by a
broken steam loco, so they often insist that a modern diesel be
coupled in behind the steamer.  (Sometimes this is also done when the
steam loco is pulling modern passenger cars, since it takes a modern
diesel to supply electric power and heat to the cars.)

--Tim (tssmith@netcom.com)



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