# Why couldn't trains draw power from the railroad tracks? **URL:** \ **Category:** Factual Questions\ **Created:** [June 13, 2014, 5:54pm UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717 "2014-06-13T17:54:58Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![rsa](https://avatars.discourse-cdn.com/v4/letter/r/839c29/32.png) [@rsa](https://boards.straightdope.com/u/rsa)\ **Post date:** [June 13, 2014, 9:08pm UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/21 "2014-06-13T21:08:54Z")
> [@Malacandra](#): > > AIUI it compares pretty well with the alternative of using a clutch and gearbox, which would obviously have to be massively strong and has inefficiency losses all of its own. Also with a diesel-electric you get to use regenerative braking. A great advantage of electric motors is that they generate maximum torque at zero RPM. Really helps to get that huge mass moving. An interesting side note is that Formula 1 cars use a Kinetic Energy Recovery System (KERS) which stores energy generated under braking to provide up to an additional 160HP for brief periods. The failure of the regenerative braking system caused the two Mercedes F1 cars to lose that extra power and to overheat their brakes during last week’s Canadian Grand Prix. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [June 13, 2014, 9:18pm UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/22 "2014-06-13T21:18:05Z")
> [@carnivorousplant](#): > > It costs less to ship by rail; the customer price is lower. Right. So why would customers insist on using trucks instead? ---
**Author:** ![Aspidistra](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aspidistra/32/3894_2.png) [@Aspidistra](https://boards.straightdope.com/u/Aspidistra)\ **Post date:** [June 13, 2014, 9:19pm UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/23 "2014-06-13T21:19:34Z")
> [@carnivorousplant](#): > > It costs less to ship by rail; the customer price is lower. That doesn’t really answer the question (which I also wonder about) “We promise we won’t use the cheaper more efficient method” - what sort of contract clause is that? Or is the issue that using all-trucks is _quicker_, since you can always go straight there? ---
**Author:** ![Giles](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/giles/32/60_2.png) [@Giles](https://boards.straightdope.com/u/Giles)\ **Post date:** [June 13, 2014, 9:22pm UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/24 "2014-06-13T21:22:17Z")
> [@carnivorousplant](#): > > I wonder what the distances involved are, and at what distances the rails are powered. > Japan also has electric commuter trains, does it not? Generally, electric trains (including subways and the shinkansen/bullet trains) in Japan are powered using overhead wires, not third rails. In particular, the shinkansen use 25,000 V AC in the overhead wires: I think there would be great problems in supplying that through a third rail. ---
**Author:** ![Gorsnak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gorsnak/32/7587_2.png) [@Gorsnak](https://boards.straightdope.com/u/Gorsnak)\ **Post date:** [June 13, 2014, 9:34pm UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/25 "2014-06-13T21:34:03Z")
> [@Aspidistra](#): > > Or is the issue that using all-trucks is _quicker_, since you can always go straight there? Even if it were the customer still wouldn’t care about the mode of transport. And so far as I know, when ordering freight services you specify when you want it at the destination, not what mode of transport the freight company will use to get it there. ---
**Author:** ![The\_Second\_Stone](https://avatars.discourse-cdn.com/v4/letter/t/bbe5ce/32.png) [@The\_Second\_Stone](https://boards.straightdope.com/u/The_Second_Stone)\ **Post date:** [June 13, 2014, 10:09pm UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/26 "2014-06-13T22:09:24Z")
> [@Aspidistra](#): > > That doesn’t really answer the question (which I also wonder about) > > “We promise we won’t use the cheaper more efficient method” - what sort of contract clause is that? > > Or is the issue that using all-trucks is _quicker_, since you can always go straight there? And how do you prove damages in a breach of contract case? I seem to recall that if the contractor substitutes something cheaper than the customer expected that there must be some diminution in value to the customer for there to be a cause of action. If I put iceberg lettuce in a reefer truck in Salinas, CA and send it to Manhattan, I suspect that putting the reefer truck on a flatbed with electricity gets it there sooner and a lot cheaper than having three drivers on the truck doing 8 hour shifts because the train can go 80 to 100 mph for 3000 miles 24/7 while the truck still has to stop. And no truck really has 3 drivers, and only a few two. A single driver can legally only drive 8 hours before resting 16. ---
**Author:** ![The\_Second\_Stone](https://avatars.discourse-cdn.com/v4/letter/t/bbe5ce/32.png) [@The\_Second\_Stone](https://boards.straightdope.com/u/The_Second_Stone)\ **Post date:** [June 13, 2014, 10:10pm UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/27 "2014-06-13T22:10:28Z")
> [@Giles](#): > > Generally, electric trains (including subways and the shinkansen/bullet trains) in Japan are powered using overhead wires, not third rails. In particular, the shinkansen use 25,000 V AC in the overhead wires: I think there would be great problems in supplying that through a third rail. Is that catenary wire copper, or can it be aluminum? ---
**Author:** ![Bozuit](https://avatars.discourse-cdn.com/v4/letter/b/edb3f5/32.png) [@Bozuit](https://boards.straightdope.com/u/Bozuit)\ **Post date:** [June 13, 2014, 10:13pm UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/28 "2014-06-13T22:13:41Z")
There are a lot of explanations here for why it can’t be done, considering that, as others have noted, something very similar _is_ done and works well. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [June 13, 2014, 10:34pm UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/29 "2014-06-13T22:34:33Z")
> [@ZenBeam](#): > > Right. So why would customers insist on using trucks instead? Which post are we speaking off? ---
**Author:** ![TheLoadedDog](https://avatars.discourse-cdn.com/v4/letter/t/35a633/32.png) [@TheLoadedDog](https://boards.straightdope.com/u/TheLoadedDog)\ **Post date:** [June 13, 2014, 10:52pm UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/30 "2014-06-13T22:52:57Z")
> [@friedo](#): > > Actually they are - not for power, but for the signalling system, which relies on detecting train axles by completing a circuit across the running rails. Depending on the system, one or both of the running rails may also be used as a ground for the third rail. This is the case for all the third rail systems in the NYC area, including the NYC Subway, Metro-North (except the New Haven line) and the Long Island Railroad. Not only that, but bridging rails is easy. It’s _insulating_ them from one another that is more difficult. There are special insulation joints between signalling “blocks”, and they can often give trouble, especially in snow, etc, even for the relatively tiny current used by the signalling system. In a traction power application, you’d need thicker joints, and you’d also have to somehow insulate down the middle of the “frog” (the X-shaped bit where the two rails cross at switches). Frogs take massive impacts, and are specially single-cast blocks of a high quality alloy. They wouldn’t survive being split in two with a line of what is essentially just resin. Edit: You’d also need to somehow isolate every wheelset on the train. This is done on model trains, but would be difficult to do while maintaining strength on the real thing. And then, that would ruin the signalling system. ---
**Author:** ![TheLoadedDog](https://avatars.discourse-cdn.com/v4/letter/t/35a633/32.png) [@TheLoadedDog](https://boards.straightdope.com/u/TheLoadedDog)\ **Post date:** [June 13, 2014, 11:18pm UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/31 "2014-06-13T23:18:29Z")
Another issue is mountains. Heavy freight trains really don’t like anything but the gentlest of grades, and adding more power doesn’t help, because the wheels will simply slip. So they drop sand. This sand can get compacted down to a quite hard coating. It’s insulating silica, and is another thing that sometimes give grief to the signalling circuits. Traction circuits would be a little more robust, but it would likely still be an issue. ---
**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:** [June 13, 2014, 11:48pm UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/32 "2014-06-13T23:48:00Z")
One other point that the OP might be missing: One conductor isn’t enough. You need two to complete a circuit. The two rails of an ordinary railroad track don’t work, because they’re connected to each other in many places, as **TheLoadedDog** just mentioned. But you can use, for instance, the rails as one leg, and a third rail or catenary wire as the other. It’s not too hard to install an overhead electrical contact on a diesel locomotive, to run on power from a catenary wire and the rails, and in some places this is done. Amtrak, for instance, uses catenary wires between Harrisburg and New York (and probably other lines, too-- That’s just the one I know about). This lets them run trains along that stretch without any pollution from the locomotives. When they get to Harrisburg, there’s a brief delay while they start up the diesels and switch over the electrical systems, and then the train continues on the route under its own power. ---
**Author:** ![Carl\_Pham](https://avatars.discourse-cdn.com/v4/letter/c/e9a140/32.png) [@Carl\_Pham](https://boards.straightdope.com/u/Carl_Pham)\ **Post date:** [June 13, 2014, 11:52pm UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/33 "2014-06-13T23:52:37Z")
> [@carnivorousplant](#): > > I wonder at the efficiency of generating electrical current with diesel motors to power the electric motors that drive the train. As opposed to what? The coal- or oil-fired electrical plant that otherwise generates the electricity to send down the wires or rails to the electric locomotive? ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [June 14, 2014, 12:07am UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/34 "2014-06-14T00:07:25Z")
> [@Bozuit](#): > > There are a lot of explanations here for why it can’t be done, considering that, as others have noted, something very similar _is_ done and works well. I don’t think people are saying “can’t” so much as explaining why it’s difficult enough that other alternatives may be preferable. In a similar vein, I could go on for pages about why orbital space stations are a pain in the ass to pull off, but I wouldn’t be implying that we can’t/don’t build them. ---
**Author:** ![MichaelEmouse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/michaelemouse/32/101_2.png) [@MichaelEmouse](https://boards.straightdope.com/u/MichaelEmouse)\ **Post date:** [June 14, 2014, 12:11am UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/35 "2014-06-14T00:11:10Z")
> [@Carl\_Pham](#): > > As opposed to what? The coal- or oil-fired electrical plant that otherwise generates the electricity to send down the wires or rails to the electric locomotive? It’s not clear what’s most efficient without looking at the power generation and distribution in detail. Yes, plants have to distribute their power in a way that implies losses. However, plants usually use a combined cycle production that gets more power out of the same energy source. > **[Combined cycle power plant](https://en.wikipedia.org/wiki/Combined_cycle)** > > A combined cycle power plant is an assembly of heat engines that work in tandem from the same source of heat, converting it into mechanical energy. On land, when used to make electricity the most common type is called a combined cycle gas turbine (CCGT) plant, which is a kind of gas-fired power plant. The same principle is also used for marine propulsion, where it is called a combined gas and steam (COGAS) plant. Combining two or more thermodynamic cycles improves overall efficiency, which reduce... But, yeah, as others have said, unless you can keep the electrified element out of the reach of animals/suicidals/drunks/idiots, don’t use it. And that’s why the extra sparky rail is seldom used for railroads. As Dracoi said in his ninja’ing post, it’s not that we can’t, it’s that we really don’t want to for good, electrified reasons. ---
**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:** [June 14, 2014, 12:39am UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/36 "2014-06-14T00:39:14Z")
> [@](#): > > Quoth **MichaelEmouse** : > > It’s not clear what’s most efficient without looking at the power generation and distribution in detail. In general, in either process the inefficiencies are going to be dominated by the step where you burn the fuel to drive a heat engine, such that whichever process has the more efficient heat engine will almost certainly be more efficient overall. Power plants will usually be more efficient than portable internal combustion engines, mostly because they can run at higher temperatures. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [June 14, 2014, 12:43am UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/37 "2014-06-14T00:43:20Z")
> [@Carl\_Pham](#): > > As opposed to what? The coal- or oil-fired electrical plant that otherwise generates the electricity to send down the wires or rails to the electric locomotive? As opposed to using a diesel engine to turn the wheels, as in a steam locomotive. ---
**Author:** ![MichaelEmouse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/michaelemouse/32/101_2.png) [@MichaelEmouse](https://boards.straightdope.com/u/MichaelEmouse)\ **Post date:** [June 14, 2014, 12:45am UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/38 "2014-06-14T00:45:59Z")
> [@carnivorousplant](#): > > As opposed to using a diesel engine to turn the wheels, as in a steam locomotive. Wut? Steam locomotives use diesel? I thought diesel engine were internal combustion whereas steam engine were external combustion. Did I get that wrong? ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [June 14, 2014, 12:55am UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/39 "2014-06-14T00:55:01Z")
> [@MichaelEmouse](#): > > Wut? Steam locomotives use diesel? I thought diesel engine were internal combustion whereas steam engine were external combustion. Did I get that wrong? Sigh. No. Consider a steam locomotive. Steam moves a piston than in various sorcerous ways, move the wheels. I was wondering why diesel engines don’t power the wheels through a transmission, as in a car or truck. Diesel locomotives work by having a diesel engine turn generators. The generators in turn power electric motors that turn the wheels. ---
**Author:** ![eltro102](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@eltro102](https://boards.straightdope.com/u/eltro102)\ **Post date:** [June 14, 2014, 1:24am UTC](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717/40 "2014-06-14T01:24:02Z")
All the trains that run in London which don’t go cross-country use third rail systems, with the DLR being fully automated A lot of the cross-country trains use overhead wires, and I don’t remember the last time I saw a big noisy diesel locomotive here. [Previous page](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717.md?page=1) [Next page](https://boards.straightdope.com/t/why-couldnt-trains-draw-power-from-the-railroad-tracks/690717.md?page=3)