Assume you can hook every locomotive and car Union Pacific owns up into a single gigantic freight train. Safety and laws aside, would it work?
In: Physics
Is it more efficient ti have one long train with multiple engines,or several short trains being pulled by 1 engine each?
There is no hard physics limit, as long as the engines are coordinated.
7.3km and 100,000 tons here:
https://web.archive.org/web/20160107175613/http://www.railwaygazette.com/news/single-view/view/bhp-breaks-its-own-39heaviest-train39-record.html
The longest train ever was 7.3 km long, comprising of 682 ore cars pushed by 8 locomotives in Western Australia in 2001.
You, five year old, can drag your red ryder sled behind you. If you let it go, the sled will come to a stop.
It comes to a stop because of this thing called friction. When two objects slide against each other, they slow down. It takes more energy to keep them moving. If you aren’t there to pull the weight, or more importantly, if you _can’t_ pull the weight, the sled would stay put.
Weight makes friction more and more of a problem. If you put some rocks in your red ryder, the weight that you’re pulling will be a lot more. You’ll pull more slowly the more weight you add, and with too much weight, you won’t be able to overcome friction and the sled can’t move at all.
A train’s engine car at the front is just like you, pulling your red ryders. A train just has a bigger engine, and can pull heavier things at faster speeds. But, just like you, trains have their limits. An engine can only pull so much freight. The more cars you add, and the more things you put in those cars, the heavier the train gets. That means it will get slower and slower, until it can’t move at all.
Now, if I can go on a tangent for a bit, the solution to this problem was successfully implemented some 70 years ago… by Walt Disney Imagineering, then known as WED Enterprises. Walt and his engineering team put together a propulsion system where the _track_ was what would provide the energy, not an engine car. This was the peoplemover system, but you might better understand it exemplified as the haunted mansion doom buggies. Each buggy is its own, self-propelled carriage, pushed and pulled along the track by a series of magnets placed at regular intervals. This isn’t a _train_ if you define a train as a single engine pulling a series of cars. But it _is_ a constant, infinite line of cars moving along a track.
There are a few cities around the world who have used peoplemover tech in their public transit system, but to this day it’s pretty rare. One reason for this is that theme park rides are non-essential. With a conventional train, the tracks are simple and the trains are complex. That means trains need repairs more often than tracks do. If you need your trains to run as much as possible, the tracks need to be reliable.
If a train or its cars need repairs, you can take that one train off the tracks without interrupting the path of other trains that use that track. When your track has a problem, and your track is filled with cars end-to-end, the entire route is blocked until the track can be fixed.
That’s not the only concern, either, but, this is already waay more than you asked for, so I’ll leave it at that. The answer is that, no, you’d have to have much, much stronger engines to pull trillions of tons worth of freight as one singular train. There are other systems that exist to get a constant stream of cars moving infinitely along a track, but those aren’t technically trains, and come with their own set of problems. Great for theme parks, though!
Technical: There’s a limit with the effective range of distributed power. It operates via radio so the lead locomotive can give directions to the mid and tail end units. My railway doesn’t like it more than three miles away because it’s a pain in the ass when it loses communication, of course cars can be added behind a DP unit and there are very open places without a lot of interference that could easily extend the functional range of DP so this is a factor but ultimately a loose peg at determining the true max length of a train.
Logistic: Trains travel between major cities, they require places to stop, sure you can stop all other traffic and send one over sized train across the subdivision but it is a massive encumbrance if you have literally 0 places your train fits across 150 miles of track, so much so that this often defines the max length for particular subdivisions.
Handling: Trains have in train forces: buff and draft. Longer trains are harder to manage particularly over more challenging terrain on a two mile long train it’s not uncommon to go over pieces of territory where the train is straddled over two or three changes in grade. It’s possible to poorly marshall (organize) a train so badly that it just cannot go across a troublesome stretch of track without breaking the train, we usually learn from our mistakes and make tedious rules to try and eliminate this kind of gross incompetence.
Equipment: You can only put so many engines online in a consist of engines, 2-5 depending on a lot of factors. You can only have so many distributed consists. So there is a hard limit on the amount of engines a particular railway can use in a single train.
Trains operate using air brakes. Have you ever tried connecting straws together and blowing through them as a child? You get leakage, you can’t suck up someone’s drink from 15 straws away without getting lots of extra air bubbles in at each of the joints, trains are kinda like that. On a nice summer day you might run 12,000ft of train to a single air source no problemo but in the cold it changes, I’ve seen it as bad as 2000ft to an air source to move.
So you take all these things I’ve just talked about and factor them all together the world record holder is likely to be: fair weathered, in a place without lots of crossings and flatter or at least smoother terrain is better. Which I believe is currently held by BHP of Australia with a 4.5 mile long train.
99,732 Tons, 682 cars, 8 x 6000hp engines, 4.5 miles in length.
As a guy who runs trains all the time there aren’t a lot of trains I’m dying to run. I wish I could run this absolute nutter of a train…just once. I’m just over here kicking the wheels on my wimpy 30,000 ton train.
The weight capacity of the locomotives
Length of passing loops (for single-track lines)
For passenger trains, the platform length at stations
The length of the train introduces some complex dynamics. There’s a small amount of play between each car, and each car has momentum.
It’s basically a long, heavy chain. You can’t push a chain. It just bunches up. You can only pull.
When you have a long train, you can have one part of it going up a hill and another part going down a hill. The cars on the downhill side want to accelerate, the cars on the uphill side want to decelerate.
If the front is climbing the hill and the rear is coming down the hill, what happens to the middle? It gets pushed by the downhill cars into the uphill cars.
If you apply the breaks to the locomotives in front and the cars behind it, what happens to the cars behind them? They risk running right into the decelerating cars and hopping the tracks.
Now expand that to every single car in the US combined into a mega train.
There are 1.6 million rail cars and 28,000 locomotives in the US . Combined they form a single train over 18,000 miles long. For reference, a flight from LA to NYC is only 2,445 miles.
So what happens when we have a 18k mile long train climbing up and down the Rocky Mountains and the Appalachians and the Sierra Nevadas? Even if we somehow found the perfect rail path that allows for a continuous 18k mile long train without running into itself, it’s going to derail all over the place. The train will need to slow down in areas, and any mistake will cause a cascade of decelerations back to the point where the train cars just can’t stop in time, and they’re pushed off the tracks.
My train obsessed 5 year old can tell you the answer to the current records for largest amount of carriages.
The longest recorded passenger train was 70 carriages. This is probably the upper limit for passenger trains due to station limitations.
The longest recorded freight train was 672 wagons and 8 engines. Freight trains can generally be longer due to them often being unloaded at ports for direct export.
As others have stated, adding a engine every few cars would allow a near infinite length (which would be similar to an infinite amount of small trains that happened to be connected together)
If we are talking about a single freight engine- (which we give infinite pulling power) how many cars can you add to it? Then we would be limited by the weight a train coupler can hold. 725,000 lbs. Then math that out vs the Rolling friction of a train track times the weight of the cars.
I’d say 480 cars(7.4km), not quite sure on the formula.
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