What decides how many locomotives for a train?

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#2
HP Assignments

Experience or formula?
Wow, big question. I'm not a motive power dispatcher, but as I understand it, there's a formula for how many horsepower to assign per ton over a particular district depending on how fast you want the train to go. Flat midwest will take less HP per ton than climbing mountain grades. A hotshot will have more HP per ton than a drag freight. Others can fill in better than I, I'm sure.
 
#4
My buddy is one of our Power Coordinators for Roseville, we call them RH1. (It stands for Round House 1) So he is the one who gets the train info then has to build the consists for the train. Here is his answer "Kinda hard to put into words...it deals with tons per axle. A loco has a ratio that each traction motor can pill. Of course the bigger the unit the more the traction motor can handle."

When I asked if it matters if the train is on flat land or mountains he said "Yes it does."

Althought this is only a half assed answer it came from the horses mouth.
 

Ed Sand

General Idiot
#6
The short answer is 'formula informed by experience'.

A particular train will have a horsepower per ton (or tons per equivalent powered axle for you younger folks) requirement. This is a fairly strict formula that depends on the terrain (grades, curves) and speed (slow freight, higher speed intermodal). If train MRVPT has 8,000 tons and requires 2.2 hpt then you need 17,600 horsepower worth of locomotives.

Usually, however, there isn't much variation, because often times the central power desk will stipulate that a certain train ALWAYS has to run with at least 2 units because those units are then needed on another train. So, even if that particular day's train tonnage may be low, you still have to send it out with 3 units otherwise the power desk will have kittens because you've now totally screwed up the outbound train planning for the next couple of terminals. And, if you've got more tonnage than normal, there isn't usually an extra unit sitting around with nothing to do, so you reduce tonnage instead.
 

ENR3809

BCR Hoghead
#8
On CN we use Hp per ton to calculate the number of locomotives to use on a train. Other factors come into play too such as restrictions on the number of driving axles. Some subdivisions only allow 12 or 18 driving axles per locomotive consist.
 
#9
Usually, however, there isn't much variation, because often times the central power desk will stipulate that a certain train ALWAYS has to run with at least 2 units because those units are then needed on another train. So, even if that particular day's train tonnage may be low, you still have to send it out with 3 units otherwise the power desk will have kittens because you've now totally screwed up the outbound train planning for the next couple of terminals. And, if you've got more tonnage than normal, there isn't usually an extra unit sitting around with nothing to do, so you reduce tonnage instead.
Also, just because there are 3 or however many locomotives in a consist does mean that they are all online and working to move the train.
 

Robert Gift

former OL presenter
#10
Thathought also occurred to me because I was the only passenger on a 20-seat commercial flight from San Francisco to Santa Barbara. I asked why they flew it rather than have me depart later or go on another airline. They needed the aircraft to depart from Santa Barbara.

Is it better to have less locomotives working harder than more working less?
Withome furnaces, it is better to have a smaller furnace working harder than larger furnace working less.
 
#11
Thathought also occurred to me because I was the only passenger on a 20-seat commercial flight from San Francisco to Santa Barbara. I asked why they flew it rather than have me depart later or go on another airline. They needed the aircraft to depart from Santa Barbara.
Seen that too, but on a much larger scale ... used to fly to Orlando a lot for work ... would fly back on Fridays. Friday = arrival day for lots of people doing 3 day mouseworld vacations ...

So this giant 777 would be sitting there, with 10 passengers, back to ATL ... where it would depart right back to Florida stuffed to the gills ...

As the UPS commercial says ... logistics ...
 
#12
Logistics and they may need power somewhere else, or deadhead to a shop for major repair. The railroad does'nt work on reason anyway, otherwise trains would all be on schedule.
I flew from Austin to Dallas. The pilot lifted off, said we are arriving DFW! Don't think we left the ground.

What time does the 11 oclock trrain for Chicago leave?
 



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