# How would a loco be selected for a train



## long_haired_david (Aug 12, 2014)

Let me explain the problem.

I have 3 different types of road loco available for a train - lets say (1960-1980 maybe - and excuse me if I get this wrong being of British extraction 

an RS-3 HP = 1,600 - Tractive Effort 61,775
a GP9 HP = 1,750 - Tractive Effort 64,750
a GP30 HP 2,250 Tractive Effort 63375

What would be the basis for selecting one or other of these. Would it be purely on HP or tractive effort? 

The reason I am asking is because I am building a freight car routing system and having generated a number of cars that need to be put on a train, I now need to select a loco to be the pm. If these three are available as road switchers, why would I choose one or the other - assuming that the load was within range?

If the load was out of range and thus needed two locos, again, what would be the criteria? (assume that we had more than one of each available).

If the question doesn't make a lot of sense, you can see where I am coming from so perhaps, in those circumstances, maybe you propose the problem in a more realistic way?

David

Main man on the S&NE


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## rkenney (Aug 10, 2013)

The only rule is: there are no rules.

Really every road is going to have a roster of tractive power to meet their needs (that they'll add to as needs change). Each loco would simply be used for maximum benefit; speed, load, range.

Your road has three engines. The RS3 is a yard engine (switcher) so you now have two choices to haul freight.

Conclusion: It's your call, they are just toys.


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## long_haired_david (Aug 12, 2014)

Firstly, I would rate the RS3 as a "Road Switcher" in the same category as the GP9 - it has only slipped a bit due to passing time. Secondly, "It's my call, they are only toys". Granted but my interest is in writing software to represent the real world. At the moment, I am not running trains - be they toys or not - so I a trying to understand the real world.
David


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## Brakeman Jake (Mar 8, 2009)

Railways are economy oriented,this is the one and only rule.When needing pulling power,they will first look at what is available then select the most economical option that will pull the load on the given territory.

They won't use a big SD90 if they have a GP40 that will get the job done.The same way they won't use three locos if two are enough.They never use motive power for the pleasure of seeing it go by like we modellers do.


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## long_haired_david (Aug 12, 2014)

Thanks but that doesn't explain the reasons. If you can tell me how they calculate that a GP40 will do, then that is what I am after.
David


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## Brakeman Jake (Mar 8, 2009)

They know the weight they have to pull and select the proper motive power.All locomotives are rated by their horsepower,speed and more important their pulling power.I'm sure other members here can tell you a lot more.


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## time warp (Apr 28, 2016)

The three locomotive examples you have given don't really represent more than one class, being that they are of comparable horsepower and would MU together.

Things like wheel arrangement (BB or CC), gearing (speed), dynamic brakes, and ballast weight all factor in, so a GP 30 actually could be very different from one to the other. Also true of the RS or the Geep 9.

My Railroad has a rule that any locomotives below 2000 horsepower must be double headed for mainline service, so that automatically dictates the power I use.
Local freight and transfer work use available power. The branchline trains use lighter switchers of around 1000 horsepower due to weight restrictions.

The 3 locos you've mentioned would probably just be doubled when more power was needed, which would be protypical.


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## DonR (Oct 18, 2012)

This can be a very technical subject.

In addition to the factors already presented
the railroad must be aware to the track conditions
on the route. Track grade is very important. Some
railroads in the past went bankrupt because the grades of their
track required too many locos to manage them.

Then too...is the inverse...if you go up, you must
come down. Dynamic braking is essential. They
must know the whole train WEIGHT and the braking
capabilities of the assigned locos to stop it. A few
years back, part of
a small California town was wiped out by a run a way
train when the planners did not take into consideration
all of the factors and didn't assign the right locos with
enough braking ability to the train.

Don


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## long_haired_david (Aug 12, 2014)

I think that we need to settle on a simple set of parameters.

There would be a divider of the HP to get the tonnage.
Example 1,750HP GP9
This could be:
0.5 for way freights =3,500 tons
1.0 for normal through freights = 1,750 tons
2.0 for fast manifest freights =875 tons.
Each route lists all the stations so:
For each sector of the route (between stations) we could add a factor. The software could then calculate a limiting factor and decide if one, two, three locos, etc. would be needed for the train.

Given that the software will never see the light of day, this would be implemented into the final report document.


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## time warp (Apr 28, 2016)

You need a base figure to build parameters from in order to "plug in" a given train and match up a specific locomotive. That will work in regards to developing a software program, but it will only be in reference to your model railroad's specification. In that case you simply use your own criteria.

The real world doesn't and can't operate that specifically. It would be completely unrealistic for a given railroad to hand pick a certain locomotive simply based on the train that needs moved. I've no doubt that there is more applied experience involved in what loco or combinations of locos are used for certain tasks than simple specifications. Case in point:
A GP 18 and an RS 11 look close on a piece of paper performance wise, but it's a proven fact that the RS11 will pull harder. You can't calculate that. So you have the old experienced engineer saying" tell them they better use the ALCO's on the old hill line, we've learned the hard way that the Geeps don't like it so well". 
Just saying, I don't think it can be calculated that specifically. Most trains are made up with too much horsepower any way, that too from practical experience.


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## thedoc (Oct 15, 2015)

Years ago I was talking to a ConRail driver and he was telling me that the operating department would assign engines to a train based on tons per axle. The problem was that 4 axle and 6 axle engines of the time had about the same HP per engine so a train with 4 axle units had much more HP than a train with 6 axle units for power. The difference was enough to effect how quickly the train could get up to speed and how fast the train could go.


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