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Tobias Benjamin Koehler (s_tbk@ira.uka.de) wrote:
: Translation of the article below:

: Does anyone know why in North America the trains have almost
: always several Diesel locomotives? Even "short" freight trains
: mostly have two locos in front. This multiple traction is more
: expensive than a single locomotive - at least in the cost of
: purchase and maintenance. Why don't they just build more power-
: ful locos? And use 1 to 3 instead of 2 to 8 locos?

: I'm sure these newsgroups can help Andreas more than the German 
: one.

: [ Article crossposted from zer.t-netz.eisenbahn ]
: [ Author was Andreas Adlhoch (a.adlhoch@jokl.pfalz.de) ]
: [ Posted on 01 May 1995 08:23:00 +0100 ]

: Hat jemand von Euch eine Ahnung, warum in Nordamerika die Z�ge fast immer  
: mit mehreren Dieselloks bespannt werden? Es ist ja sogar so, da� "kurze"  
: G�terz�ge meistens zwei Loks vorne dran haben. Diese Mehrfachtraktion ist  
: doch auch teurer, als eine einzige Lok - in den Anschaffungs- und  
: Unterhaltskosten zumindest. Warum bauen die dann nicht einfach st�rkere  
: Loks??? Und fahren anstatt mit 2 bis 8 Dieselloks nur mit 1 bis 3 Loks?

: --                  _,-'"`-._           _,-'"`-._  le progr�s ne vaut
:  tobias b. k�hler   `-.___,-'. .-.-.-. .`-.___,-'     que s'il est
:  s_tbk@ira.uka.de   --=========================--   partag� par tous
:                       |]||[]|   [___]   |[]||[|
:     >______-----------| ||  |   13254   |  || |-----------______<
:   |_|    ==   ==___== | ||__| =   =   = |__|| | ==___==   ==    |_|
:  >|_|-------__(-)-(-)__--|__|-----------|__|--__(-)-(-)__-------|_|<
: (=|_|__| *_/__\_(o)_/__\__/_ \ |_|=|_| / _\__/__\_(o)_/__\_* | ||_|=)
:    / (*)   \__/ ~~~ \__/  \__/   -^-   \__/  \__/ ~~~ \__/   (*) \

The short answer is, because most North American railroads are
still using fairly low powered locos, because they feel it is
more economic to maintain the ones they bought in 1960, or
buy second-hand ones, than to buy the monolithic, high tech
diesels that are currently on the market. This is gradually
changing, as it becomes more and more expensive to service
the older units. Canadian freight carriers have been "playing"
with the newer units, leasing them and ordering small quantities.
On the other hand, they continue to lease huge numbers of SD40's,
GP35's and GP40's from private leasing companies. CPRS even
had Morrison Knudsen rebuild some Southern Pacific SD45's
they had purchased, but *downgrading* the internals to
SD40 standards. This is probably because they are already
tooled to service SD40's. On the other hand, they have
ordered 25 or so huge GE Dash 9's, as have Canadian National.
Well, that answer is too long.. the short answer is,

"because they are too darn stingy to buy anything new".

--
  ____________   __________________
   |  |[]|  |   |][] # # # # ## [][|
 |_|__|__|__|_| |_||_________## ||_|   Ken Willmott
_|=_oo____oo_=|__(UUU)`------'(UUU)________________

>Tobias Benjamin Koehler (s_tbk@ira.uka.de) wrote:
>: Translation of the article below:
>
>: Does anyone know why in North America the trains have almost
>: always several Diesel locomotives? Even "short" freight trains
>: mostly have two locos in front. This multiple traction is more
>: expensive than a single locomotive - at least in the cost of
>: purchase and maintenance. Why don't they just build more power-
>: ful locos? And use 1 to 3 instead of 2 to 8 locos?
>
>: I'm sure these newsgroups can help Andreas more than the German 
>: one.
>
>: [ Article crossposted from zer.t-netz.eisenbahn ]
>: [ Author was Andreas Adlhoch (a.adlhoch@jokl.pfalz.de) ]
>: [ Posted on 01 May 1995 08:23:00 +0100 ]
>
>: Hat jemand von Euch eine Ahnung, warum in Nordamerika die Z�ge fast immer  
>: mit mehreren Dieselloks bespannt werden? Es ist ja sogar so, da� "kurze"  
>: G�terz�ge meistens zwei Loks vorne dran haben. Diese Mehrfachtraktion ist  
>: doch auch teurer, als eine einzige Lok - in den Anschaffungs- und  
>: Unterhaltskosten zumindest. Warum bauen die dann nicht einfach st�rkere  
>: Loks??? Und fahren anstatt mit 2 bis 8 Dieselloks nur mit 1 bis 3 Loks?
>
>: --                  _,-'"`-._           _,-'"`-._  le progr�s ne vaut
>:  tobias b. k�hler   `-.___,-'. .-.-.-. .`-.___,-'     que s'il est
>:  s_tbk@ira.uka.de   --=========================--   partag� par tous
>:                       |]||[]|   [___]   |[]||[|
>:     >______-----------| ||  |   13254   |  || |-----------______<
>:   |_|    ==   ==___== | ||__| =   =   = |__|| | ==___==   ==    |_|
>:  >|_|-------__(-)-(-)__--|__|-----------|__|--__(-)-(-)__-------|_|<
>: (=|_|__| *_/__\_(o)_/__\__/_ \ |_|=|_| / _\__/__\_(o)_/__\_* | ||_|=)
>:    / (*)   \__/ ~~~ \__/  \__/   -^-   \__/  \__/ ~~~ \__/   (*) \
>
There are probably a number of different reasons, but one may 
be that a locomotive can not exert a pulling force greater than about one 
fourth of its weight unless it has anti-slip computer control of its 
motors, in which case it can exert a pulling force of about one third of 
its weight.  Those forces are on dry sanded track; on wet track the 
forces are reduced.  Therefore if the railroads wanted to reduce the 
number of locomotives to half the present number, their weight would have 
to double to pull the same loads.  I question whether tracks and trucks 
are engineered to take such loads.

BF

   : Does anyone know why in North America the trains have almost
   : always several Diesel locomotives?

   The short answer is, because most North American railroads are
   still using fairly low powered locos, because they feel it is
   more economic to maintain the ones they bought in 1960, or
   buy second-hand ones, than to buy the monolithic, high tech
   diesels that are currently on the market. 

I think this is a distorting the situation somewhat.

The newest highest-tech units on the market today are around 5000
horsepower (most just a little under that).  While this is a good deal
more than the 3000 HP of the SD-40-2's that dominated the scene just a
few years ago, it's not enough more to make a difference in many
situations.

The original poster was from Europe, where I understand short fast
trains are the norm.  Over here the preferences seem to favor longer
trains, often using 7-8 units for power.  I've seen a large number of
UP trains (Columbia River valley, across the river from Wishram,WA)
with 7 of those modern high-tech C40-8W units.  That's 28,000 HP, give
or take a little.  There's no way that a single locomotive could be
built using today's technology that would be this powerful.  One of
the major limiting factors is the load that can be placed on the
traction motors.  The current generation of traction motors are much
better than older ones, but not enough so to handle 28,000 HP.

Even if it could be done, what then happens when that units fails.
You have a 28,000 HP unit down until it's fixed, instead of one of 7
4,000 units.  6 4000 HP units can probably bring the train into the
next siding, clearing the line for other traffic.  

On another end of the spectrum, the older units that are very common
on shortlines and regionals are there because it's uneconomical to
replace them with new units.  Even if they could afford to buy a new
4000 HP unit ($2 million, as opposed to a few older GP's or SD's for a
few hundred thousand apiece), the track plant might not be suitable
for a single locomotive as large as these new units are.  They're
*heavy*, and many branchlines cannot support that kind of weight.

So in many cases the shortlines can't afford the new stuff, and the
big railroads *are* buying the newest high-tech units, but that still
won't make a single locomotive powered mainline train feasible.

-- 
 david d `zoo' zuhn   | Armadillo Zoo Enterprises, St. Paul, MN
 zoo@armadillo.com    |  unix generalist (and occasional specialist)
                      |  http://www.armadillo.com/ for more info
 

In <3oa2s6$1co@nz12.rz.uni-karlsruhe.de> s_tbk@ira.uka.de (Tobias
Benjamin Koehler) writes: 
>
>Translation of the article below:
>
>Does anyone know why in North America the trains have almost
>always several Diesel locomotives? 

 [snip]

Of course, one notable exception would be the Road Railer trains
frequently pulled by a single loco because of the overall lighter
weight of the train.

Peter

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Peter G. Chase, Columbus, OH, USA              CompuServe:72732,2307
Internet:pchase@ix.netcom.com

In article <3oa2s6$1co@nz12.rz.uni-karlsruhe.de> a.adlhoch@jokl.pfalz.de writes:
>Translation of the article below:
>
>Does anyone know why in North America the trains have almost
>always several Diesel locomotives? Even "short" freight trains
>mostly have two locos in front. This multiple traction is more
>expensive than a single locomotive - at least in the cost of
>purchase and maintenance. Why don't they just build more power-
>ful locos? And use 1 to 3 instead of 2 to 8 locos?
>
>I'm sure these newsgroups can help Andreas more than the German 
>one.
>

Probably right, Toby.  Well, as best I recall...

In North America, there have been attempts to use fewer larger locomotives to
haul trains, with the ultimate example being Union Pacific's monster DDA40X
"Centennial" locomotives, rated at 6900 horsepower.  These were not much more
than two uprated GP40s in a single unit, with large rigid trucks.  (In fact, a
similar, earlier unit, the DD35/DD35A, was nicknamed the "5000 horsepower track
straightener" due to its long, rigid four-axle trucks.)  However, despite the
fact that these DID deliver a great deal of power, it was found that there were
several problems with it.  For one thing, if the locomotive was disabled by a 
mechanical fault, it put the equivalent of two smaller locomotives out of 
service.  Also, with such a unit, there was a great deal less flexibility--by
using 3000 horsepower units, you can tailor the power to the train much more
easily.  The smaller the units, the less excess horsepower you'll need to put on
the train, and the less cost you'll have, since those bigger, more powerful
units do burn more fuel even at a lower power setting...

It's interesting to note that another horsepower race is developing, and the
most powerful new locomotive being advertised is the GE AC6000CW, which will
provide 6000 horsepower.  I have to wonder if the railroads will discover the
problems of single huge locomotives again...

RM
(FINALLY done with finals!)

-- 
A! JW2 YK++i WK++i DT++ PI++i BR+++I SL++ SK RI++ RU+ GDF GP+++
GLF BU MI----------- HIP------------- SN+ HN+! RL++ PL- WB? CB~
ME MM---! KK---------------------------------------------------
CO Tinker P++ Dadoopfo Tow $++ E35 T191(Slappy) Ay76 M

In article <3oa2s6$1co@nz12.rz.uni-karlsruhe.de>, s_tbk@ira.uka.de 
says...
:Does anyone know why in North America the trains have almost
:always several Diesel locomotives? Even "short" freight trains
:mostly have two locos in front. This multiple traction is more
:expensive than a single locomotive - at least in the cost of
:purchase and maintenance. Why don't they just build more power-
:ful locos? And use 1 to 3 instead of 2 to 8 locos?
:
:I'm sure these newsgroups can help Andreas more than the German one.
:
:[ Article crossposted from zer.t-netz.eisenbahn ]
:[ Author was Andreas Adlhoch (a.adlhoch@jokl.pfalz.de) ]
:[ Posted on 01 May 1995 08:23:00 +0100 ]

In addition the the other responses about low powered locos...

North American rail cars weigh from 30 tons empty to 140 tons loaded.

Also, a group of locomotives may remain coupled together for an entire
work shift, even though pulling vastly different numbers of cars 
thoughout the day.  An SP local out of Warm Springs (California) always
has a pair of 3000HP locos, even when pulling only 5 cars on flat rail.
Part of the same day may be spent pulling 20 loads up a 1% grade.

-Dave

Tobias Benjamin Koehler (s_tbk@ira.uka.de) wrote:
: Translation of the article below:

: Does anyone know why in North America the trains have almost
: always several Diesel locomotives? Even "short" freight trains
: mostly have two locos in front. This multiple traction is more

Well, I see about 30% of trains on the Toronto subdivision
pulled by a single unit. These have few cars, though.

: expensive than a single locomotive - at least in the cost of
: purchase and maintenance. Why don't they just build more power-
: ful locos? And use 1 to 3 instead of 2 to 8 locos?

In addition to what others have posted, consider this-
North American locos are single cab. If you put two together
long hood to long hood, you can change direction and still
have the cab in front without turning the consist.

--
  ____________   __________________
   |  |[]|  |   |][] # # # # ## [][|
 |_|__|__|__|_| |_||_________## ||_|   Ken Willmott
_|=_oo____oo_=|__(UUU)`------'(UUU)________________

In <3oa2s6$1co@nz12.rz.uni-karlsruhe.de> s_tbk@ira.uka.de (Tobias
Benjamin Koehler) writes: 
>
>Translation of the article below:
>
>Does anyone know why in North America the trains have almost
>always several Diesel locomotives? Even "short" freight trains
>mostly have two locos in front. This multiple traction is more
>expensive than a single locomotive - at least in the cost of
>purchase and maintenance. Why don't they just build more power-
>ful locos? And use 1 to 3 instead of 2 to 8 locos?
>


The factors involved are:

1. Weight of train.
2. Ruling grade levels on the territory to be traveled.
3. Horse power to axle rating of the locomotive.
4. The low speed continuous tractive effort of each unit in kilopounds 
   of drawbar.
5. The type of train being pulled.


For example, an intermodal train would have more power than a heavier
coal train because the intermodal tain needs to run at a higher speed.
It also needed a faster exceleration ratio so that it can reach and
hold its higher speed quicker. Most intermodal trains have a horse
power to ton rating of about 4 HP/ton. Most of these trains on CSX use
four axle units account of acceleration. A 3600 HP unit has a 900 HP to
axle rating providing high acceleration compared to a 3600
six axle unit with 600 HP per axle.

On the other hand, heavy drags like coal, grain, rock, and manifest
freight, do not need the acceleration rate as high, so you see more
6 axle power to overcome the heavier weight. Most 90 unit coal trains
have a HP/ton rating from 0.7 to 1.0.

As for more powerful engines, you could take one 4000 HP four axle unit
and start pulling a 1000 ton train. A 1500 HP unit would be able to
start the same train as well, but the 4000 HP unit can pull it at a
higher speed. This is where HP comes in, in speed. You will see 6 axle
units on these trains because their higher tractive effort is used to
overcome the greater weight.

In article <3oanmm$id3@sunburst.ccs.yorku.ca>, yku01468@afep.yorku.ca 
(Kenneth Willmott) attributes the large number of locomotives on 
U.S. trains to:

> The short answer is, because most North American railroads are
> still using fairly low powered locos, because they feel it is
> more economic to maintain the ones they bought in 1960, or
> buy second-hand ones, than to buy the monolithic, high tech
> diesels that are currently on the market.

  The major railroads in the US all have orders with the two big
producers of locomotives... Electromotive Division of General Motors
and General Electric.  However, because there are so many units
on order, there is a pretty serious backlog, and the locomotive
builders can't keep up with the demand.  Case in point... Conrail
is assembling SD60Is at its shops in Altoona, Pennsylvania, because
EMD can't build them fast enough.  Lots of units are being delivered
in primer to other roads because they can't get 'em through the paint
shop quick enough.  The boom in traffic that stimulated this huge 
demand for power has left many lines power short.  To alleviate the
power shortage, locomotive lessors have been having a heyday renting
out engines that railroads had gotten rid of during leaner times.
A good example of this is the Burlington Northern, which has leased
formerly-owned power from smaller carriers.

My $0.02 worth!

P.J. Hinton
Graduate Student--University of Notre Dame Chemical Engineering Department

INTERNET: P.J.Hinton@nd.edu

It was written:

: Does anyone know why in North America the trains have almost
: always several Diesel locomotives? Even "short" freight trains
: mostly have two locos in front.

In many cases, it is to prevent the train from being stranded if one loco dies.
If most trains had only one or two very powerful units, they'd be in trouble
if one broke down.  There was an article in Popular Mechanics awhile back 
(around Christmas, I believe), that talked about the New/Rebuilt 6000 hp diesels
Morrison Knudsen was making for the SP (the exact name escapes me at the 
moment).  They talked about the future of diesel horsepower, and said that the
horsepower rating per unit will not go very far above 7000, because, among 
other things, of the above concern I mentioned.

- Rob

In article <3ob9i8$odm@butch.lmsc.lockheed.com>,
Dave Herzstein <dherzstein@lmsc.lockheed.com> wrote:
>In article <3oa2s6$1co@nz12.rz.uni-karlsruhe.de>, s_tbk@ira.uka.de 
>says...
>:Does anyone know why in North America the trains have almost
>:always several Diesel locomotives? Even "short" freight trains
>:mostly have two locos in front. This multiple traction is more
>:expensive than a single locomotive - at least in the cost of
>:purchase and maintenance. Why don't they just build more power-
>:ful locos? And use 1 to 3 instead of 2 to 8 locos?
>:
>:I'm sure these newsgroups can help Andreas more than the German one.
>:
>:[ Article crossposted from zer.t-netz.eisenbahn ]
>:[ Author was Andreas Adlhoch (a.adlhoch@jokl.pfalz.de) ]
>:[ Posted on 01 May 1995 08:23:00 +0100 ]
>
>In addition the the other responses about low powered locos...
>
>North American rail cars weigh from 30 tons empty to 140 tons loaded.
>
>Also, a group of locomotives may remain coupled together for an entire
>work shift, even though pulling vastly different numbers of cars 
>thoughout the day.  An SP local out of Warm Springs (California) always
>has a pair of 3000HP locos, even when pulling only 5 cars on flat rail.
>Part of the same day may be spent pulling 20 loads up a 1% grade.
>
>-Dave
>

There is an excellent article in the back of "The Contemporary Diesel Spotter's
Guide" (Kalmback Books) on requirements on horsepower, traction effort, 
etc. that dictate the number, size, horsepower, etc of engines.  Since
most main-line freight trains are over a hundred cars of well over 100 tons, 
moving at over 50 mph, you need at least 4 3000 hp locos even on level
terrain.  Add some grade and you start to need to cut in two or three helpers.  

The article also addresses how railroads of different management styles
might wind up with different fleets for the same requirements.

Peter Mason

In article <3ob3k0$lk2@msunews.cl.msu.edu>, mannin16@egr.msu.edu (uid no access) says:
>
>In article <3oa2s6$1co@nz12.rz.uni-karlsruhe.de> a.adlhoch@jokl.pfalz.de writes:
>>Translation of the article below:
>>
>>Does anyone know why in North America the trains have almost
>>always several Diesel locomotives? Even "short" freight trains
>>mostly have two locos in front. This multiple traction is more
>>expensive than a single locomotive - at least in the cost of
>>purchase and maintenance. Why don't they just build more power-
>>ful locos? And use 1 to 3 instead of 2 to 8 locos?
>>
>>I'm sure these newsgroups can help Andreas more than the German 
>>one.
>>
>
>Probably right, Toby.  Well, as best I recall...
>
>In North America, there have been attempts to use fewer larger locomotives to
>haul trains, with the ultimate example being Union Pacific's monster DDA40X
>"Centennial" locomotives, rated at 6900 horsepower.  These were not much more
>than two uprated GP40s in a single unit, with large rigid trucks.  (In fact, a
>similar, earlier unit, the DD35/DD35A, was nicknamed the "5000 horsepower track
>straightener" due to its long, rigid four-axle trucks.)  However, despite the
>fact that these DID deliver a great deal of power, it was found that there were
>several problems with it.  For one thing, if the locomotive was disabled by a 
>mechanical fault, it put the equivalent of two smaller locomotives out of 
>service.  Also, with such a unit, there was a great deal less flexibility--by
>using 3000 horsepower units, you can tailor the power to the train much more
>easily.  The smaller the units, the less excess horsepower you'll need to put on
>the train, and the less cost you'll have, since those bigger, more powerful
>units do burn more fuel even at a lower power setting...
>


I also heard somewhere that one of the reasons that the DD35 and DD40's were
not widely ordered was that at about that time the improved electronics that
went into the -2 series (GP38-2, GP40-2, SD40-2, etc.) greatly reduced some
of the problems and failure points associated with running long MU'ed loco
sets. So it became easier and more reliable for the RR to run 2 GP40-2's, 
rather than one DD35 or DD40. Plus, they had the option of splitting the 
pair of smaller locos to run alone or add to another pair (to make a 
threesome), if necessary.

I'm no expert on the electronics involved, so if I'm wrong, please correct 
me. Like I said, this is just something I read somewhere.


Paul Noble                  | God does not play dice with
NASA Lewis Research Center  |  the universe - Albert Einstein
Cleveland, Ohio 44135       | Not only does God play dice 
xxnoble@wpogws.lerc.nasa.gov|  with the universe, sometimes
                            |  he throws them where we can't
                            |  see them - Stephen Hawking