How many freight cars can a train pull?

Question

Does it have to do with Total GWT? or Cars per engine?

Answer 1

Hoghead Ia totally correct --  it's all a factor of HP/ton.  Here in the Midwest, we have a railroad that uses two locomotives per train, irregardless of length; but for their inter-modals, they assign 3-4 hp/t

Answer 2

A train consists of one or more locomotives pulling a string of cars.  So a train doesn't "pull cars."  A train IS cars.  A locomotive or locomotives pull cars.

Many factors affect the answer.  The maximum number where locomotives are of high horsepower and the engineering of the rail line is good is between 100 and 150 typical cars.

Answer 3

Hoghead gave the best answer, and I can tell he is the genuine locomotive engineer!

How many cars a train can pull is a poorly asked question.  A "train" by official definition is an engine with or without cars with a dispatcher-issued clearance and showing a marker (usually a red flag or red light).  A yard engine is not a train unless it has received a clearance and displays a marker.  When I ran helper engines "light over the hill" to help another train, I had a clearance form and displayed a rear headlight to serve as my marker.

There is an additional term called "string-lining".  Southern Pacific had a great railroad until they were changed in corporate structure over to SPTC (Southern Pacific Transportation Company), and all of a sudden Harvard and Yale management types came to tell experienced railroad executives how to run a railroad!  (ahem.)

Up in the Shasta line and around Redding California, the "new management" got the bright idea of not using the helper formula: add the road locomotive horsepower to the helper horsepower, divide that into the total weight of the train for the tons to be handled by each engine (an engine is one or more locomotives multiple-unit connected), and then the mid-train helper pulls 2/3 of its assigned tonnage and shoves 1/3 of its assigned tonnage.  The "new management" decided it was stupid having two crews, so they put all of the horsepower on the "head end".

The result is that the overpowered head end locomotives pulled the cars in the first part of the train right off the tracks and into the lake!  Take a piece of string (from which this term comes from), put it in a u-shape.  Now pull one end.  Does the string follow around in line?  No.  It pulls straight.  That is what happened to the trains.  This is a key to just one factor as to how much of a train that locomotives can pull.

Another is air brakes.  I've run one 250 car train, and whenever you touch the automatic air brake handle, you absolutely have to stop the train completely before you can release the brakes and recharge the train before moving.  There is no way you can release the brakes at the rear of the train until you wait about a half hour for the compressors to recharge the air brake line.

The Louisville and Nashville ran a 500 car coal train with one road engine and five helpers.  They could not keep it moving due to normal air leaks in the trainline.  As soon as the train would move, several miles up the line the cars would undulate and the gladhands would leak and the brakes would set up.  Unlike trucks, with railroad trains, you lower the brake pipe air pressure to set the brakes, and you increase the brake pipe air pressure to release the brakes, a really great safety mechanism.  This is done through what is called an "automatic brake valve" located in each engine and car to route air to each car's air reservoir, but I will not get into the technicalities of that.

On Southern Pacific's Los Angeles Division between Los Angeles and Yuma Arizona and West Colton to Bakersfield, we pretty much were limited to around 125 cars and ten locomotives per engine.  Helpler engines rarely had more than four locomotives or units and usually went mid-train, sometimes "on the point".  Behind the caboose, we could not have more than twelve axles powered.  Sometimes we did have almost 150 cars over Beaumont Hill, but very rarely, and always with mid-train helpers.

Another factor not related to horsepower or tractive effort is the railroad's physical characteristics and traffic density.  Can a long train be safely run from one end of the division to another without causing a conflict due to the train being longer than a siding?  The crossover for Mons Siding and Fingal Siding were connected together so that the two sidings were made into one very long passing track.  Sometimes, with two moderate size trains and the right timing, on the downhill train we could enter Mons Siding and "get in the clear" and slow way down and make a running meet without stopping at the bottom of Fingal Siding, provided we had a clear understanding with the dispatcher, and, it was usually the dispatcher who called us over the radio to set the move up.

I think that Hoghead gave the best and most accurate basic explanation, however.

Ronald Kinum

a.k.a. Libris Fidelis

[e-mail]

Answer 4

There are some trains in the US which are over a half mile in length, although I have not seen one in the UK longer than 500 yards

Answer 5

It has more to do with horsepower per ton, whether or not there is a DPU, and the territory over which the train is traveling.  A loaded DPU coal train can pull 136-140 loaded coal hoppers.  Usually there is about 12-13000 horsepower, and a train like that weighs about 13-14000 tons.  Usually you don't want any less than about .8 hp/ton.  But if the territory has a lot of short hills, there could be restrictions on length.  The prior mentioned coal train is about 75-7700 feet long, and if it is really hilly, there is the chance of knuckles breaking, or worse (if you have a green engineer), draw bars breaking.  I have heard of DPU intermodal trains that have up to 180 cars, but they are rare.

Answer 6

in the us ive seen a single midsize loco pull around 50 full hoppers they have a max weight of 199000 lbs each the bigger boys can pull 80 per engine thats alot of weight them things pull if you think of it and do the math around 20 million lbs in that entire train rolling thru your town

Answer 7

Railroad standard since railroading began goes somethign like

"Uphill slow, downhill fast, tonnage first and safety last"

I'm being facetious of course but that statement is scribbled on yard office walls the country over.

The limiting factor is tonnage, or as you state GWT. The weight of cars varies from 25 tons to well over 130 and I have worked on locomotives with horsepower ratings everywhere from 600 to 5500.

However Hoghead is correct, ultimately, if you connect enough locomotives together to pull the tonnage, the limiting factor is length. According to wikipedia the longest train with no supplemental air source for the brake system is 7.3 KM, in Australia. My math is rusty at this time of day but I'm pretty sure that is a bit over 4 miles.

Where I work we have what they like to call "undulating serpentine grade", (or lots of curves, hump and bumps)

The least horsepower we can nominally get by with is about .6 horsepower per ton.

(yes, that's right 6/10 of a horsepower per ton of train, that's why trains are so much more fuel efficient than any other forms of land based transportation.

So, take an average 3000 horsepower locomotive pulling empty cars at 32 tons each and on the run I am assigned to one locomotive can pull around 56 cars at the very maximum.

This will vary from territory to territory so as you can see from the answers above, there is no set answer.

Answer 8

A locomotive with a string of cars is a train. I think you mean how many cars can a locomotive pull - and that depends entirely on the locomotive, but will depend on the total weight of the cars and the dbhp of the loco.

Answer 9

For clarification, a "train" is, by definition, "An engine, with or without cars, displaying marker."

The factors that determine tonnage limits, and therefore numbers of cars that can be pulled, include gross trailing tonnage, horsepower per ton, grade and curvature and in some instances, weather plays a factor.

When determining power requirements for a given run the "Rolling Train Resistance Formula" comes into play.  It is, horsepower per ton, multiplied by 12, divided by the percent of the grade equals the speed that train will make.  Put another way, HPT x 12 / %G = Speed.

Speed is important in that below 12 mph, the locomotives may run into their "short time" rating while handling tonnage up-grade.  This is a figure that tells us how long we can run the engine under extreme conditions without the traction motors over-heating.  If the short time rating is exceeded severe damage to traction motors and cabling thereto can result.  But, short time ratings are not cumulative nor constant.

So, the number of cars that can be handled is variable.  SP ran some 200 car freight drags with "repeater air cars" cut into the train in the 70's, but they just didn't work.

But, in terms of practicality, 110 cars or so is reasonable and usual when railroading in grade territory.

The factor that really imposes the number of cars for any given run is train length.  When running single (no helper or DPU's cut into the train) when the train length exceeds 9,000 feet or so, funny things start hapenning with the air brakes.  In addition trains are usually no longer than the longest siding on the district, lest they become a "non-clearing" train.  In single track operations, this makes dispatching trains more of a challenge.