21–26 of 26 posts
>But rail is a pretty safe way to get around (more so than driving Understatement of the year. Even in the US the number of deaths per year averages around half a dozen; you're about ten times as likely to be killed by a bolt of lightning. From a people-safety perspective, encouraging people to use trains by making them convenient will have an overwhelmingly better impact than trying to improve train safety. Not that…
Earlier quoted context omitted.
I've always wondered if, in the age of high-speed bullet trains, it is possible to use the pair of rails as a transmission line, send a pulse down the track, and measure the distance to the next obstacle by the reflection. Of course they use the rail as an electrical ground, though, which could be an issue.
I don't see why you couldn't. You're basically describing a time-domain reflectometer. But it is correct for you to say "to the next obstacle" rather than "to the train". The next obstacle could be a switch, or perhaps a line welded on for the signaling system. It could even be a broken rail.
The problem is that detecting that serves no purpose, and you need to detect past those joins for it to serve a use.
The crumple zone point in the article misses the mark. The reason why crumple zones don't exist on American railways is due to incompetent and centuries-out-of-date Federal Railroad Administration regulation. FRA insists on railcars being able to withstand 800,000 lb of pressure without deformation, the so called "buff strength" requirement. This works OK for low speed gondolas and goods vans making up the bulk of th…
Outdated regulation plays a part, particularly around the assumptions of where loads come from. As you mentioned, the buff crushing load assumes a longitudinal action only. Moreover, there has historically been minimal roll-over strength in cabins to protect pasengers. Change is disappointingly slow, however, and with asset lives of 50+ years due to the tough financial challenges facing particularly passenger rail, it takes a long time for new regulation to come into practice.
Earlier quoted context omitted.
I don't see why you couldn't. You're basically describing a time-domain reflectometer. But it is correct for you to say "to the next obstacle" rather than "to the train". The next obstacle could be a switch, or perhaps a line welded on for the signaling system. It could even be a broken rail.
Track joins mess with that sort of thing. They serve two purposes: 1) to insulate between sections of the aformentioned short-across-rails signalling system, 2) to allow for the thermal expansion/contraction of track due to temperature. Even without 1, you still need 2 and that will interfere with sending any signal down the track. The problem is that detecting that serves no purpose, and you need to detect past thos…
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You're right that track circuits are simple and relatively reliable, but they are also inefficient. Having to retain sufficient safety margins while being unaware of the real location of trains means that there is excess "dead space" in each signalling block that could be used to drive more trains over the existing infrastructure. It's what happens with systems like the DLR in London, which uses an advanced moving bl…
So have tighter blocks more often. A block is a discretization of the continuous track, and in track-space, your absolute "GPS" location isn't relevant -- just where you are on the track. The on-vehicle location detector ("GPS") is essentially a cost-effective alternative to having infinitesimally small, fixed blocks. The benefits are equivalent: the tradeoff is between whether you want to spend money on maintaining…
The modern systems generally prevent this. See [1] for an exception -- the engineers forgot to install the limiting markers at the very end of the high speed line, allowing the train to overspeed into the normal speed line.
[1] https://en.wikipedia.org/wiki/Santiago_de_Compostela_derailm...
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NYC Subway is really hard-core about train stops. There's a trip cock on every subway car, near the right front wheel, and it works by directly operating an air valve to the brakes. The train stop lever alongside the track is raised by a big spring and lowered electrically, and the signaling system senses when it's physically up, ready to trip. Only then can the preceding train stop lower. There are always several tr…
WOW! That Chicago story is straight up bizarre. Thanks for sharing that. I'm not sure, though, that dumb train control is necessarily the answer. The Chicago system looks pretty dumb (though I know nothing about it), certainly no more complex than the New York system, but the fact that the CTA system self-reset seems to imply it cannot be safe without a human in the cab. This misfeature is a problem regardless how du…
I hope the US doen't get stuck with inventing something itself. It would certainly cost more. 20 or so non-European countries have started to use this system[1], including some very large ones.