# 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:** 13\ **Page:** 3
**Author:** ![Peremensoe](https://avatars.discourse-cdn.com/v4/letter/p/ce7236/32.png) [@Peremensoe](https://boards.straightdope.com/u/Peremensoe)\ **Post date:** [November 6, 2015, 9:48pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/41 "2015-11-06T21:48:41Z")
> [@iceiso](#): > > 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?”. Everybody leave a bigger gap in front of you when you stop, and we can all get going quicker. ---
**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, 9:52pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/42 "2015-11-06T21:52:14Z")
> [@Dorjan](#): > > 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? You are not paying attention. Air pressure, from the engine, gets pumped into the clamping cylinder. The clamping cylinder is passive: all it does is push the shoe toward the drum. It has no control valve. Air is then sent into the opposing release cylinder, which pushes the shoe off the drum. If the train separates, the air line to the release cylinders in the lost cars gets broken open, air comes off the release cylinder, the trapped pressure in the clamping cylinder applies the brake. Over time, probably on the order of hours, a clamping cylinder that does not get steadily refreshed will eventually leak air until its pressure normalizes and the pressure on the brake comes off. ---
**Author:** ![Dingbang](https://avatars.discourse-cdn.com/v4/letter/d/ac8455/32.png) [@Dingbang](https://boards.straightdope.com/u/Dingbang)\ **Post date:** [November 6, 2015, 9:54pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/43 "2015-11-06T21:54:57Z")
nm ---
**Author:** ![Tired\_and\_Cranky](https://avatars.discourse-cdn.com/v4/letter/t/a87d85/32.png) [@Tired\_and\_Cranky](https://boards.straightdope.com/u/Tired_and_Cranky)\ **Post date:** [November 6, 2015, 10:04pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/44 "2015-11-06T22:04:31Z")
Thanks \*\*Dorjän \*\*for asking the question I wanted to ask and **eschereal** for answering it so clearly. One other question though, why not just use a spring to provide the clamping force on the brake and opposed air pressure to push the friction surface off the drum? Then, if air pressure failed, the brakes would all clamp shut and the train would not move until the pressure was either reapplied or the brakes were mechanically, manually released. Would it be too hard to build a spring that provides enough clamping force for the job? Or would the spring tension fade over time, weakening the brakes? Would the brakes be too hard to modulate? ---
**Author:** ![Dingbang](https://avatars.discourse-cdn.com/v4/letter/d/ac8455/32.png) [@Dingbang](https://boards.straightdope.com/u/Dingbang)\ **Post date:** [November 6, 2015, 10:08pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/45 "2015-11-06T22:08:10Z")
I’m really trying to pay attention here, but this liberal arts major still has a question: If both sides of the braking action – open and closed – require air pressure, wouldn’t it be better to have the closed action be purely mechanical? Something like a big spring that forces the brake against the drum unless it is opposed by air pressure? Then if the brakes lose air pressure, suddenly or over time, the default action is always braking. Wouldn’t that be more of a safety default than something that requires air pressure on both sides of the equation? ---
**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, 10:20pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/46 "2015-11-06T22:20:51Z")
As I anecdoted earlier, we were able to move a loaded rail car with about a dozen people. If braking were a strictly mechanical force, that would not have been possible. Having rail cars that are set in place, unmovable, may not be the ideal 100% of the time. And a yard bull can move cars around yards and sidings (short distances, slowly) without having to pressurize the braking system. Also, springs have a fairly finite lifespan, after which they are junk (recyclable). Compressing springs eventually makes them not want to spring back, and rail cars spend a considerable portion of their life in motion, during which the springs would be getting weary. You do not want to abruptly discover that your braking springs are worn out. Making durable, long-lasting braking springs adds weight to each car, which would be better served to go to payload. ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [November 6, 2015, 10:30pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/47 "2015-11-06T22:30:02Z")
> [@Hari\_Seldon](#): > > They are trying to pin the whole fiasco on the engineer. Of course. That’s highly improper: the engineer was off-duty in the hotel, and so survived the incident. They are supposed to blame someone who is dead, and so isn’t around to raise inconvenient objections. Here in the USA, our FAA has perfected this technique – nearly all plane crashes are blamed on “pilot error”. Even ones clearly due to defective equipment – they say “the pilots should have noticed this in their pre-flight inspection, so it’s their fault”. So the FAA never has to worry about dealing with airlines or airplane manufacturers, who are still around and who have lots of lawyers. Just blame it on the dead pilot. ---
**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, 10:44pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/48 "2015-11-06T22:44:53Z")
Another issue with having a mechanical spring/compressed air release setup is that dragging brakes are potentially almost as hazardous as the brakes failing. If the brakes are just dragging on a single car while the train is underway, it won’t be immediately apparent to the train crew but can cause the brakes to severely overheat, causing something similar to that old railroader’s nightmare the [hot box](https://en.wikipedia.org/wiki/Hot_box). ---
**Author:** ![Muffin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/muffin/32/4341_2.png) [@Muffin](https://boards.straightdope.com/u/Muffin)\ **Post date:** [November 6, 2015, 10:49pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/49 "2015-11-06T22:49:10Z")
> [@Hari\_Seldon](#): > > They are trying to pin the whole fiasco on the engineer. Of course. There is plenty of blame to go round on this one: government regulations, government enforcement, company management/operations, and yes, the engineer. For folks interested in the particulars, have a boo at the [Transportation Safety Board report](http://www.tsb.gc.ca/eng/rapports-reports/rail/2013/r13d0054/r13d0054-r-es.asp) and the [Wiki page](https://en.wikipedia.org/wiki/Lac-M%C3%A9gantic_rail_disaster#Technical_investigation). ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [November 6, 2015, 10:54pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/50 "2015-11-06T22:54:03Z")
> [@t-bonham@scc.net](#): > > … nearly all plane crashes are blamed on “pilot error”. Even ones clearly due to defective equipment I’d be interested in hearing of an example where defective equipment was classified as pilot error. (My view is that this is probably rare.) > [@](#): > > … they say “the pilots should have noticed this in their pre-flight inspection, so it’s their fault”. Well, that’s kind of what pre-flight inspections are for - to catch potential problems. ---
**Author:** ![Rysto](https://avatars.discourse-cdn.com/v4/letter/r/ecccb3/32.png) [@Rysto](https://boards.straightdope.com/u/Rysto)\ **Post date:** [November 6, 2015, 10:57pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/51 "2015-11-06T22:57:04Z")
I would expect that another advantage of 5 locomotives and 500 cars in the train is that if one locomotive breaks down, the other 4 can still keep the train moving rather than shutting down the rail line entirely until a working locomotive can be dispatched (which is what would happen with 1 locomotive pulling 100 cars). I would expect modern locomotives to be quite reliable but I would imagine that breakdowns will happen from time to time. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [November 6, 2015, 11:17pm UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/52 "2015-11-06T23:17:56Z")
> [@Hari\_Seldon](#): > > 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. From the TSB report: > [@TSB of Canada](#): > > The TSB looked very carefully at single-person train operations, and at whether having just one crew member played a role in the accident. After looking at the circumstances that night, the investigation was not able to conclude that having another crew member would have prevented the accident. > [@Hari Seldon](#): > > They are trying to pin the whole fiasco on the engineer. Who is? > [@TSB of Canada](#): > > This report identifies 18 distinct causes and contributing factors, many of them influencing one another. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [November 7, 2015, 12:05am UTC](https://boards.straightdope.com/t/economics-of-train-length/736777/53 "2015-11-07T00:05:40Z")
> [@eschereal](#): > > The clamping cylinder is passive: all it does is push the shoe toward the drum. It has no control valve. Air is then sent into the opposing release cylinder, which pushes the shoe off the drum. That’s kind of how the brake system _acts_, but not exactly how it _works_. In reality there is only one cylinder/piston. There is a complicated “triple valve” that connects the brake line to the reservoir and the cylinder. When the line pressure is higher than the reservoir pressure, the valve directs air from the line to the reservoir (to pressurize the reservoir), while at the same time venting the brake cylinder (i.e. disengage the brake). When the line pressure is lower than the reservoir pressure, the valve connects the reservoir to the cylinder, applying the brake. There is a [good explanation with clear diagrams here](http://www.railway-technical.com/air-brakes.shtml). When it comes to applying a _huge_ amount of force on demand, it’s hard to beat pneumatic or hydraulic systems. It’s a very simple force multiplier - like a lever, but easier to construct because there is very little stress on the whole system _except_ the piston that does the actual work. With a mechanical lever, stress is concentrated at the fulcrum. With a hydraulic or pneumatic system, all the plumbing can be at moderate pressure, and still apply a huge force on the piston if the piston is big enough (force = pressure \* area). [Previous page](https://boards.straightdope.com/t/economics-of-train-length/736777.md?page=2)