# Economics of Train Length **URL:** \ **Category:** Factual Questions\ **Created:** [November 6, 2015, 3:46am UTC](https://boards.straightdope.com/t/economics-of-train-length/736777 "2015-11-06T03:46:08Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 6, 2015, 1:25pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/21 "2015-11-06T13:25:27Z")
There’s yet another reason to make trains longer that nobody has mentioned yet: Air resistance. The air resistance of an object depends mostly just on its cross-sectional area, and not on how long it is. So if you make a train twice as long, you increase the air resistance only slightly, not by a factor of 2. ---
**Author:** ![robert\_columbia](https://avatars.discourse-cdn.com/v4/letter/r/e79b87/32.png) [@robert\_columbia](https://boards.straightdope.com/u/robert_columbia)\ **Post date:** [November 6, 2015, 1:35pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/22 "2015-11-06T13:35:10Z")
> [@Tripler](#): > > If I recall a discussion correctly, I learned that each of the cars has a constant brake applied to its wheels. The locomotives power a compressed air system that holds the brake pads off of the wheels when the train is in motion. If the Engineer needs to stop quickly, he releases the pressure off that system, and the brake pads are reapplied to each car’s wheels. It’s a reverse system from your auto, which requires hydraulic pressure to apply brakes; trains hold brakes off with an active pneumatic system… The main advantage to this is that it provides a fail-safe layer. If the train breaks apart in motion, cars that have become disconnected from the engine will lose air pressure in their brake systems causing them to automatically apply their brakes. This helps prevent “runaway train” situations. [Here’s](https://www.youtube.com/watch?v=jB_pB7lDDpI) a video of this happening. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [November 6, 2015, 1:59pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/23 "2015-11-06T13:59:40Z")
One other point: For safety & routing, trains need to be scheduled to be a certain distance apart. One long train still takes up only one slot in the schedule. As for the limit of train length - I notice there are still many single-track railways in the US. Those require passing loops, where trains coming from opposite directions meet and pass each other. This obviously sets the limit for the length of the train. I’m not sure what the limiting factor is for trains travelling only on double-track lines. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 6, 2015, 2:06pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/24 "2015-11-06T14:06:12Z")
> [@](#): > > As for the limit of train length - I notice there are still many single-track railways in the US. I’m not sure that “still” is the right word, there: A lot of tracks that used to be double have been reduced to single. I expect that this is due to improvements in communications and planning, that make it easier to coordinate the use of the passing loops. ---
**Author:** ![Boyo\_Jim](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)\ **Post date:** [November 6, 2015, 2:22pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/25 "2015-11-06T14:22:03Z")
Nobody’s mentioned yet that the destination of each car has to be taken into account. They’re not all going to be going the same direction, and this will inevitably affect the size of lots of trains. ---
**Author:** ![Diceman](https://avatars.discourse-cdn.com/v4/letter/d/22d042/32.png) [@Diceman](https://boards.straightdope.com/u/Diceman)\ **Post date:** [November 6, 2015, 2:42pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/26 "2015-11-06T14:42:44Z")
One other factor, that probably does apply to your location: Many municipalities have laws limiting how long a railroad crossing can be blocked by a train, and the railroad will get fined if this limit is exceeded. If a town along the track doesn’t allow crossings to be blocked for longer than (say) 10 minutes, then a 500-car train would probably take too long to cross. ---
**Author:** ![Hermitian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hermitian/32/470_2.png) [@Hermitian](https://boards.straightdope.com/u/Hermitian)\ **Post date:** [November 6, 2015, 2:49pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/27 "2015-11-06T14:49:02Z")
Ok, here is something no one mentioned: the couplings. Shouldn’t that limit how long a train can be? If the engines are all at one end, they must exert a very large force on the couplings to pull all those cars. ---
**Author:** ![robert\_columbia](https://avatars.discourse-cdn.com/v4/letter/r/e79b87/32.png) [@robert\_columbia](https://boards.straightdope.com/u/robert_columbia)\ **Post date:** [November 6, 2015, 2:54pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/28 "2015-11-06T14:54:22Z")
> [@Chronos](#): > > I’m not sure that “still” is the right word, there: A lot of tracks that used to be double have been reduced to single. I expect that this is due to improvements in communications and planning, that make it easier to coordinate the use of the passing loops. If you look at satellite images of railroads, you can sometimes see the faint remnants of removed tracks. [Here’s](https://www.google.com/maps/@39.4586478,-77.9606007,223m/data=!3m1!1e3) an example in West Virginia where you can see faint scars on the ground where tracks used to lead to the (now decommissioned) roundhouses. I imagine that the primary reason for tearing up tracks is that keeping them there requires maintenance and that maintaining those tracks has become cost-inefficient. In other words, it costs more to maintain the tracks than those tracks make. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [November 6, 2015, 2:57pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/29 "2015-11-06T14:57:17Z")
> [@Hermitian](#): > > Ok, here is something no one mentioned: the couplings. Shouldn’t that limit how long a train can be? If the engines are all at one end, they must exert a very large force on the couplings to pull all those cars. They don’t put all the engines at one end for very long trains. You’ll often see several engines at the front, and additional engines in the middle and/or the back end. All controlled from the operator at the front. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [November 6, 2015, 3:05pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/30 "2015-11-06T15:05:32Z")
> [@scr4](#): > > … As for the limit of train length - I notice there are still many single-track railways in the US. Those require passing loops, where trains coming from opposite directions meet and pass each other. This obviously sets the limit for the length of the train. I’m not sure what the limiting factor is for trains travelling only on double-track lines. All true. But here’s an interesting bit of train nut trivia … Given a single track with a single double-ended passing siding of length X, it’s possible for one train shorter than X to pass another train longer than X going the opposite direction. That’s pretty obvious if you think a bit. What’s surprising is that it’s possible (with enough finagling) for two trains both longer than X to pass in opposite directions using the same single passing siding that is only X long. In fact both trains can be arbitrarily longer than X, i.e. 3x, or 4x length even. The difficulty & time involved starts big and goes up stupidly as the trains get above 2X. But it can and has been done when track outages or other exigencies require the maneuver. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 6, 2015, 3:49pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/31 "2015-11-06T15:49:28Z")
That would involve both trains stopping, and a lot of decoupling and recoupling, wouldn’t it? EDIT: Oh, and the other reason to tear up unneeded tracks is that steel is expensive. If a rail company can sell off nearly half of their tracks for scrap, they could bring in a big chunk of money. They might even be able to re-use the ties for something. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [November 6, 2015, 4:27pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/32 "2015-11-06T16:27:10Z")
> [@Chronos](#): > > That would involve both trains stopping, and a lot of decoupling and recoupling, wouldn’t it? … Yes it does. It’s sort of the railroading equivalent of those topological transform tricks like taking off your vest without removing your waistcoat. And like the dog walking on two legs, the wonder isn’t that it’s done well but that it’s done at all. Here’s an explanation of how to do it for two trains each with X \< length \< 2X. [http://www.sdmrra.org/Odds-n-Ends/saw\_bye.htm](http://www.sdmrra.org/Odds-n-Ends/saw_bye.htm) It generalizes a lot like a \*\*Towers of Hanoi \*\*problem. And with similar efficiency :D. ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [November 6, 2015, 6:21pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/33 "2015-11-06T18:21:16Z")
> [@dtilque](#): > > You’d think these brakes would be used on all trains. Unfortunately they are not, as the town of Lac-Mégantic can testify. No, no, that is not what happened at Lac Megantic. The pressure on the air breaks gradually dissipates when the engine is shut off. What happened at Lac Megantic is, like most such accidents, a combination of circumstances. Since the question of the OP has been adequately answered, I will hijack this thread and give my own explanation (but based on various and sometimes conflicting reports). 1. The company asked permission from the Conservative government to cut down from a two-man crew to one man. 2. The Conservative government, answering to its true masters, acquiesced to that request. 3. The engineer worked about a 16 hour shift. Then stopped the train on a hill and prepared to go to bed. 4. Each car, in addition to the air breaks has a hand break. To set a hand break, you have to climb up the ladder to the top of the car and then turn a crank some number of turns (not sure how many, but it is work). The exhausted engineer set about half as many hand breaks as guidelines called for. 5. He also left the engine running, which should have kept the air breaks set. 6. Then he went to bed (in a nearby hotel). 7. A fire broke out in the locomotive. 8. Firemen came and extinguished the fire and also turned the engine off. 9. Thereby the air breaks gradually loosened. 10. All hell broke loose. They are trying to pin the whole fiasco on the engineer. Of course. Sorry for being so tendentious, but this is how I see it. –Hari ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [November 6, 2015, 6:28pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/34 "2015-11-06T18:28:37Z")
```php ``` > [@SpyOne](#): > > Well, they’ve been doing multi-locomotive trains for over a hundred years, and this only applies recently, but: > on modern trains, you can link the controls of multiple locomotives together. So 5 locomotives essentially become 1 locomotive with 5x the power. And the savings there is only one driver, instead of 5. Being able to control multiple locomotives from a single cab has been around since the earliest diesels. What _is_ a relatively new development is [distributed power](https://en.wikipedia.org/wiki/Distributed_power), which allows locomotives anywhere in the train to be controlled from the cab up front. That’s important because: > [@Hermitian](#): > > Ok, here is something no one mentioned: the couplings. Shouldn’t that limit how long a train can be? If the engines are all at one end, they must exert a very large force on the couplings to pull all those cars. This. Before distributed power became common, the biggest limiting factor was the amount of draw bar pull the couplers near the front of the train have to endure, particularly in mountainous regions. With DP, though, there’s not really any physical limit to how long trains can be. A few years back, Union Pacific got in some trouble for running a monster 3.5 mile long intermodal train as a “test” through parts of southern California without telling anyone: [http://articles.latimes.com/2010/jan/13/local/la-me-monster-train13-2010jan13/2](http://articles.latimes.com/2010/jan/13/local/la-me-monster-train13-2010jan13/2) ---
**Author:** ![iceiso](https://avatars.discourse-cdn.com/v4/letter/i/3be4f8/32.png) [@iceiso](https://boards.straightdope.com/u/iceiso)\ **Post date:** [November 6, 2015, 6:34pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/35 "2015-11-06T18:34:21Z")
I’ve often wondered, when sitting at a traffic light with 20+ cars in front of me, “wouldn’t it be nice if when the light turned green, we could ALL floor the pedal (assuming we all had the same car), and all come up to full speed in several seconds?”. Instead, I’m left at a complete stand still, waiting for each person in front of me to assess an increasing buffer between them and the car in front of them. 30 seconds after the light turned green, and I still haven’t moved! I’d imagine that the 1 locomotive with 500 cars is like the former, while 5 locomotives with 100 cars is the latter. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [November 6, 2015, 7:17pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/36 "2015-11-06T19:17:23Z")
With distributed power, could it be practical, using multiple crews, to build (put together) a train in such a way that it would cross the country and live-break sections (at locomotives) as sets of cars approach their destination? ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [November 6, 2015, 7:37pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/37 "2015-11-06T19:37:22Z")
If you don’t have distributed locomotives there is also an issue of the pull trying to straighten curves. This causes the ties to shift sideways in the ballast a bit, and eventually has to be corrected. ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [November 6, 2015, 7:48pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/38 "2015-11-06T19:48:51Z")
A spring brake works on a dual chamber. One chamber uses a heavy spring to engage the brake and needs to be charged with air to release the spring. The other chamber is activated by air to apply the brakes when needed. I know on trucks they use a reservoir on each trailer and the controls in the cab are used to activate a relay valve which can quickly send air from the reservoir to the wheel. ---
**Author:** ![Snnipe\_70E](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)\ **Post date:** [November 6, 2015, 8:33pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/39 "2015-11-06T20:33:19Z")
> [@Joey\_P](#): > > That’s the opposite of how it works. Pressure keeps the brakes off. It’s designed as a fail-safe. If a line ruptures, the train stops. If part of the train where to disconnect, that section would stop instead of continuing down the line on it’s own, etc. > > As for how they pushed it, either someone pumped up the system in that car beforehand or there’s a manual release lever of some kind. My vote is for the former. Manual release. Ever notice the wheel on the back of train cars with a chain connected to it. Crank that wheel and it releases the brakes. ---
**Author:** ![Dorjan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dorjan/32/12440_2.png) [@Dorjan](https://boards.straightdope.com/u/Dorjan)\ **Post date:** [November 6, 2015, 9:34pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/40 "2015-11-06T21:34:04Z")
> [@Hari\_Seldon](#): > > No, no, that is not what happened at Lac Megantic. The pressure on the air breaks gradually dissipates when the engine is shut off. What happened at Lac Megantic is, like most such accidents, a combination of circumstances. Since the question of the OP has been adequately answered, I will hijack this thread and give my own explanation (but based on various and sometimes conflicting reports). > > 1. The company asked permission from the Conservative government to cut down from a two-man crew to one man. > > 2. The Conservative government, answering to its true masters, acquiesced to that request. > > 3. The engineer worked about a 16 hour shift. Then stopped the train on a hill and prepared to go to bed. > > 4. Each car, in addition to the air breaks has a hand break. To set a hand break, you have to climb up the ladder to the top of the car and then turn a crank some number of turns (not sure how many, but it is work). The exhausted engineer set about half as many hand breaks as guidelines called for. > > 5. He also left the engine running, which should have kept the air breaks set. > > 6. Then he went to bed (in a nearby hotel). > > 7. A fire broke out in the locomotive. > > 8. Firemen came and extinguished the fire and also turned the engine off. > > 9. Thereby the air breaks gradually loosened. > > 10. All hell broke loose. > > They are trying to pin the whole fiasco on the engineer. Of course. > > Sorry for being so tendentious, but this is how I see it. > > –Hari I must still be missing something here. If the Westinghouse system uses pneumatic pressure to keep the brakes OFF, a slowly leaking air reservoir should result in the brakes being applied tighter and tighter, not the other way around? [Previous page](https://boards.straightdope.com/t/economics-of-train-length/736777.md?page=1) [Next page](https://boards.straightdope.com/t/economics-of-train-length/736777.md?page=3)