Surely the intent of a "trapped vehicle sensor" is exactly what it says - identify a vehicle that is "trapped" ie stuck on the level crossing for some reason, not try to prevent accidents in the scenarios described.
I'm sure that sensor circuitry includes a delay before it triggers to allow for very slow moving vehicles and extra long vehicles - one wants to detect if a vehicle is disabled and sitting on the crossing and not trip an alarm for slow moving traffic.
As to the legal 20 second minimum time to activate the crossing signals before the train arrives.
Any idea when that number was established and if it is being regularly reviewed to determine if it is still applicable.
The extra long trailer trucks that were allowed a few years back were hopefully taken into consideration when establishing that 20 second interval.
On 2013-04-14, at 10:43 PM, midrly wrote:
> Consider a heavy vehicle or school bus stopped for a public crossing and then proceeding over it slowly. Even with twenty seconds' warning, it is possible for a train to strike that vehicle when it is is in the process of crossing the track.
> This is not a new issue. In 1968, a British Rail passenger train struck a truck loaded with a transformer on a level crossing that had just received automatic warning devices--
> Although this partly was a result of the trailer moving slowly over the crossing, the TSB has alluded in a report of theirs to there not being enough warning to long vehicles to allow them to clear the crossing. Just about every truck trailer is 53' long nowadays, and two of the these trailers are hauled behind a tractor between Toronto and Montreal. Unless these truck trains do not pass over ANY public crossings, the danger is patently obvious given the requisite 20 second warning for automatic crossing protection. If Highway 401 is closed for any reason, these truck trains have to use the EDR routes over public crossings.
> In November, 1994, a VIA train struck a truck on a level crossing in Quebec--
> Both of these involved transport trucks. But even scarier to me is the prospect of a school bus stopping per the law at a public crossing, then accelerating over the crossing and being struck by a train that has happened on the crossing circuit just as the bus fouls it.
> Or on an unprotected crossing at the foot of a hill over which the approaching train gives the required twenty seconds' 14L whistle signal which is not enough time for an accelerating school bus to clear it. One of these crossings is on a shortline two blocks from my house--and a school bus uses it on weekday mornings.
> Steve Lucas.
> --- In Canadian-Passenger-Rail@yahoogroups.com, "James" <unionrouting@...> wrote:
> > 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.
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