Determining How Many Locomotives Are Needed for Freight Trains?

[NJCurmudgeon]

I would assume there is a real life formula for working out how many locomotives are needed to pull a given freight train. And I would assume that would take into consideration the weight of the train, horsepower of the given engines, and the terrain (permitted speeds; hilly, flat, both). And I would further assume that it might sometimes be advantageous to have two locos back-to-back to allow easier running around the train for reverse movements.

But is there a similar rule of thumb for the world of Trainz? Thanks!

 

[cascaderailroad]

Norfolk Southern has a habit of running trains, short on power, as few units are available at a terminal.

I have seen them run a train with only 2 locos, head end, that obviously won't make it up a 1.75% gradient, and they tell them to make it as far as they can, and if they stall, passing helpers will be cut off, and hooked onto their stalled train.

Trainz physics is sometimes not as realistic as the prototype, and can take 12 locos to pull a 137 car train

 

[Dermmy]

Simple - horsepower per ton! The required horsepower varies by classification of the train - hot intermodals get more power than drag freights over the same trackage - and mountainous terrain gets more horses than flatland routes.

Rough rule of thumb? 0.5 to 1 hp/ton on drag freights on flat routes, 2.5 hp/ton is getting extreme even on a hot intermodal on a mountainous route....

 

[nfitzsimmons]

Simple - horsepower per ton! The required horsepower varies by classification of the train - hot intermodals get more power than drag freights over the same trackage - and mountainous terrain gets more horses than flatland routes.

Rough rule of thumb? 0.5 to 1 hp/ton on drag freights on flat routes, 2.5 hp/ton is getting extreme even on a hot intermodal on a mountainous route....

But how accurate is this in Trainz?

 

[Dermmy]

Should work - most recent locos have enginespecs that are as close to 'realistic' as folks can get them and DEM based routes should have close-to prototypical grades. The rest is down to the physics model, but it's not too shabby either.

If in doubt stick another unit or two on the head-end, the screenies will look better that way, though I gotta say there is a bit of a tendency to slap a ridiculous amout of horsepower on Trainz routes at the moment. A real road uses the minimum horsepower required to get the job done. Fuel ain't cheap.....

 

[Azervich]

Actually,

Horse Power doesn't mean a thing when moving trains as the engine turns a generator which supplies current to the motors geared on the axles, only time Horse Power would be counted is for getting the engine to it's maximum rpm while fighting resistance on the main Generator, Railways calculate how much can be moved based on the tractive effort of a locomotive, where I live we use 10mph continuous rating and not the actual starting tractive effort as locomotives can also slip, continuous rating at a certain speed means you'll have 90% traction with a 10% chance of slipping.

a locomotive with 40,000lbs at 10mph can move 560 tons on a 1in48 Grade, a locomotive with 30,000lbs at 9mph can move 432tons on a 1in48 grade, so what we do is work out how heavy the train is and the grades on route and working out how much a locomotive can pull, going below continuous rating is a 50% chance of slipping and stalling the train, so we allow some free tons so we don't stall, you've also got track conditions too which can change.

The number of powered axle also helps in calculating how much a loco can pull, above the 40,000lbs is 6x axles while the 30,000lbs is 4x axles.

Cheers.

 

[cascaderailroad]

One could always make a test route incline, with a mile long flat and level running start track, and a 12 mile long gradient of @ 1.75%, and test out a consist to see when, and where it stalls out.

On the Horseshoe it was pretty much ironed out by trial and error, testing if a train would stall

 

[boc61]

I've wondered about this myself. I'm not a numbers guy and would never want to bother doing the math but it is an interesting thought. I just ran the "Mojave to Bakersfield " session and was surprised to see 5 locos up front and one on the back end.

Too bad there wasn't some sort of calculator in Surveyor where you could put down a consist and get a recommendation for locomotive placement.

 

[mjolnir]

Actually,

Horse Power doesn't mean a thing when moving trains as the engine turns a generator which supplies current to the motors geared on the axles, only time House Power would be counted is for getting the engine to it's maximum rpm while fighting resistance on the main Generator, Railways calculate how much can be moved based on the tractive effort of a locomotive ... <snippage> ...

Actually, horsepower does mean a thing when moving trains. Yes, the diesel power plant is used to power a generator, but the current supplied by the generator to the traction motors is a function of the horsepower supplied to the generator. True enough, too, that more energy is needed to accelerating, than to maintain a cruising speed. There may also be a cultural issue involved here. I understand from other sources that horsepower per ton is commonly used metric in the US, but would not be in the least surprised that in other areas, the tractive effort method described by Azervich, who is not in the US, might not be the governing metric.

Further, while I won't deny that some railways may use tractive effort supplied by the locomotive, I know from direct personal experience that during the diesel era, the Rock Island based power requirements for a given train on horsepower per ton. The power center, which controlled the distribution of all locomotives on trains system wide had a book which was privately published, and copies of which were provided to whomever needed it in the field listing the amount of tonnage which could be pulled by any given type of locomotive over any subdivision over which that class of locomotive might operate. There were, where necessary, two listings for each class of locomotive on any given subdivision, one in one direction, and the other in the opposite, since ruling grades were sometimes different in different directions. When a train was assembled, the estimated total weight of the train (calculated by assuming each empty weighed 30 tons, and each load weighted 30 tons plus the weight of the load) was determined, and the number of units was assigned based upon the power that was available, either by consulting the power book, or by dividing horsepower by the number of tons.

ns

 

[Dermmy]

Actually,

Horse Power doesn't mean a thing when moving trains....

Granted, but HP/Ton is quick, easy calc that most folks can get their head around - sheesh the hp is in the name of more than half the locos out there and a single right-click will give you the tonnage - and assuming you are working on 1 hp/ton for a drag freight and 2 hp/ton for a hot job, most folks can arrive at the loco requirement without even a calculator. Most! Whatever - the result is a realistic lash-up at the head of a train. If I wrote an essay on tractive effort most folks would simply think "Huh? What?..." and move on. In fact I did write such an essay recently in response to one of those silly twenty-loco screenshots pointing out that you needed to add more locos just to hold the weight of the locos on the pictured 3% grade! Guess what - must folks thought "Huh? What?..." and moved on!

It's the KISS principle....

 

[rweber95]

Selecting locos for a consist

If you want a little more than a rule of thumb, consider this.The following is a summary of info from Al Krug's site at http://www.alkrug.vcn.com/rrfacts/hp_te.htm which I recommend you read.
Sizing the locomotive power required for a consist requires several steps and is best explained by an example.
Assume a consist weighing 15,000 tons is to be moved over a route that has a max incline of 1%. The math in this example is done for you and the notes at the bottom shows how it was done.
If the consist is stopped on that 1% incline, gravity would produce 20 lbs of force acting back down the track for each ton of weight (1.) for a total of 300,000 lbs (2.). To keep the consist from rolling back down the incline requires a locomotive with a TE (tractive effort) of 300,000 lbs. TE of a locomotive depends on the weight of the loco and the adhesion of the wheels on the track. Assuming an adhesion of 25% the required loco weight is 1,200,000 lbs (3.) . The max allowable weight on each steel wheel on a steel rail is 35,000lbs or 70,000lbs per axle. The required number of axles on the set of locos is therefore 1,200,000/70,000 = 17.14 or 18. The minimum number of locos for this consist is then three 6 wheel diesels provided that the total weight of the three locos is 1,200,000lbs. The SD70MAC weighs 420,000lbs and has 6 axles which fits this requirement.
Notice that horsepower (HP) hasn't even been mentioned yet. HP output of a loco depends on the throttle setting. The total HP required is the TE of the loco times the maximum speed desired. Assume the consist is to be pulled up the 1% incline at 15 MPH. The total HP required is 11,455 HP (4.). The SD70MAC is rated at 4000 HP so 3 locos will provide the required HP with a little to spare.

Notes:
1. (1 ton=2,000 lbs X .01=20 lbs per ton)
2. (15,000 tons X 20 = 300,000 lbs.)
3. (300,000/0.25 = 1,200,000 lbs.)
4. (300,000 lbs. X 1.4 ft/sec per mph X 15 mph/550 ft-lbs/sec = 11,455 HP.)

 

[Lots_Trains]

Very interesting discussion, I to must recommend Al Krugs web site a wealth of info there.

Now in real life this is how Locos are assigned to a train on BNSF and UP but I would say its also true for CSX and NS. Every Route in the US has a power requirement for a certain number of standard rated powered axles per per train based on the weight of the train. Now every Loco in the US has a powered axle rating, ie. a SD70 is rated a 11 axles an SD90 is 12.5 and ES44 is rated at 14. (these are the approx values from memory, I've temporarily lost my piece of paper). Hence the train is made up of what ever units are available to meet the axle requirement. Also take into account the DPU requirements I'm not 100% sure of these, I do know that anything over 8,000ft in length the DPU's must be cut into the train because of radio continuity problems.

So tractive effort does play a big factor, a SD70 has a 4400hp motor same as a ES44 but because of better trucks and software it can get its power onto the rails way better hence the higher axle rating . Mind you beware an ES44 C4 is a different story all together.

If its just a hp thing why would all the development of new high traction trucks, and special non slip software.

Another big thing in railroads for last couple of years, if you want to operate trains in realistic fashion, is all the railroads in the US are absolutely hell bent on reducing fuel consumption, with all sorts of rules coming into play. Such as throttle Max Notch 5 or 50mph which ever is less. or max notch 6 or 40mph. only trains exempt from are the Z trains.

Cheers

Lots

 

[jjanmarine3]

Hi guys. Sorry if I am a wee bit off topic but some may find it interesting.
Some trainzers may not know that every RR has a freight book for each region which has all the info stipulating all conditions that govern the hauling of loads like traction required, max permissable axles , what types of commodities are allowed , how the train must be set up etc. A driver or guard is responsible for checking their loads before departing and I have seen them refuse to take overloads and wrongly marshalled trains etc. Might be nice to have a book or info like that for trainz for each railroad...for the trainzers who are technically minded..
I was involved in technical training on diesels and a few years ago a new successful concept was introduced in South Africa called the 'Slim Kabel' - the 'Clever Cable'.
The control box was mounted in the cab, all the MU cables were modified and any combination of loco's could be shutdown and/or started up as required in a consist to cope with the conditions and for saving fuel.
A series of LED lights would show which locos are in what state at any given time on a trip.Driver are required to sign a road knowledge book every few months and they know the locos and lines like the back of their hands like we know our vehicles.
Cheers guys.

 

[NJCurmudgeon]

Many thanks for all the replies to this thread! I learned a bit not only about Trainz, but about the real life railroads too!

 

[jjanmarine3]

to add something else that I think is interesting is that when one increases the notches on the regulators gradually , rather than going to full throttle quickly, the control reaction and acceleration times of the locomotives improve.
Watch how the A1 drivers do it too, ( I know they crook the books ) they like throttle 5 on the diesels and on the steam locos the regulators are hardly ever full open.
Some of the steam locos don't like running at full cut off and actually start stalling.
The relevant specs used in trainz is actually amazingly realistic in cab mode IMO although there are a few locomotives that are either too sexy for their shirts or too lazy to work
When I get bored I start messing with the physics and push things to the limits and beyond, I find it is great fun too.

 

[SuperSpeedMaglev]

There's 3 things I'd say it needs to be able to do.

1.Get moving.
2.Have Good Braking
3.Be able to go up slopes

Braking is very important with freight trains, if you're not careful, the brakes could fail and you'd have a disaster waiting to happen.

 

[NJCurmudgeon]

I have a string of four DASH 9s on a long coal train. Notch 2 gets it started smoothly and then I can drop to 0 and it coasts a good distance before the speed slows to where I need to give it some stick again. But that's with no up or down grades. I'm using a Jointed rail locomotive and I don't know how prototypical the physics are. But I have noticed it takes fewer notches with four than two engines. What I find striking in this thread is just how many factors people have identified as part of the formula!