Minggu, 14 April 2013

Re: [CanPassRail] PTC was Perceived Risk on Various Modes


The problem with that approach is in determining if the vehicle is actually stuck on the tracks, or if is just passing over them. Even then,

Consider that in North America, the crossing circuits are set to operate for only 25 seconds or so. (20 seconds is the legally required minimum) In some cases, where there is a traffic signal preemption at nearby intersections, the crossing circuits might activate up to 45 seconds ahead of the trains' arrival at the crossing.

Consider also that a semi truck might take five or ten seconds to completely clear a crossing at low speed. That means, if the truck is just starting past the crossing signal when it begins to function, it might still be occupying the tracks only 10 or 20 seconds before the arrival of the train, under current designs. If you can see ahead from the train, such as while riding in the dome car, you will frequently see cars and trucks driving across the tracks only a short distance ahead of the train.

Now consider that a train operating at full speed, e.g. 60 mph for freight, or 100 mph for passenger, requires something like 90 to 120 seconds to come to a full stop with a very heavy brake application. How do you reconcile the two?

If you want to avoid having the brakes applying all the time just in case, which would be totally frustrating, you would have to activate the crossing circuits more than two minutes before the arrival of the train, with enough additional time to determine if the vehicle will move off the crossing, plus the time for the problem to be communicated to the affected train to apply the brakes, which wouldn't be instantaneous, given that other trains might be in the area. It also would be cheap to equip the 250 or so crossings on the Montreal - Toronto route, as just one example.

Again, the technology exists, but how much is the extra safety worth? The technology also exists to keep cars from running red lights, but we don't mandate that on vehicles, nor do we mandate sobriety or fatigue testing equipment, nor video cameras or event recorders, in spite of the technology being available and there being 2000 or so deaths a year on the highways. In other words, just because the technology exists doesn't mean that it is necessarily justified. There have to be some additional criteria to make such a decision.

--- In Canadian-Passenger-Rail@yahoogroups.com, David Jeanes
> However, when Sweden introduced the X-2000 high-speed train, they increased the speed allowed at level crossings to 200 km/h by placing trapped vehicle sensors into the road surface, by linking these sensors to the PTC system that Swedish Railways already had, and by installing magnetic track brakes on the X-2000, (subsequently also used on the German ICE trains), so that the trains could stop in time.
> The most serious accidents involving the TGV trains in France have also occurred at grade crossings where heavy road vehicles were disabled on grade crossings, (not on the high-speed lines).

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