Exit gates never crossed my mind since I have seen those for years and even then only once or twice.
I was just picturing the worst case scenario which of course should be covered off.
Something like this:
Vehicle approaches crossing
Lights start to flash - 20 second (or 22 second) interval starts
Roads are slippery, driver decides he can't stop safely in time - it's actually not critical in his mind that he tries to stop since he won't be hitting anything if he doesn't.
So "x" seconds later the front of the vehicle passes the crossing gate.
Say at this point the gates have just started to go down.
That's the 15 second point of the 20 second interval.
Vehicle is a standard tractor-trailer with a low bed trailer, crossing is in poor shape which seems to be the norm now-a-days, at least here in Montreal
So driver slows to a crawl.
10 seconds later the gates are down completely, ie 5 seconds minimum before the train arrives.
Worst case at this point (assuming the vehicle is still crossing without incident, is that the rear end of the vehicle isn just past the crossing gate.
So now there are 5 seconds to move that complete vehicle out of the path of the oncoming train.
You mentioned that you have been working with crossings for 30 years, has that interval always been 20 seconds as far as you remember?
With the much longer vehicles today than even 10 years ago, if nothing else, the interval between the signal activation and start of the gates lowering should be revisited and maybe made longer especially if the 20 second time was initially determined empirically.
That's all I'm saying.
On 2013-04-16, at 1:25 AM, Don Thomas wrote:
> Knot, your conclusion that there are only 10 seconds to clear the crossing
> appears to be based on an assumption that there will be exit gates operating
> at the same time as the gates at the entrance to the crossing. These are not
> common, but when they exist they operate later than the entrance gates. So
> any vehicle already on the crossing has 20 seconds to clear (actually 22
> seconds since there should always be a minimum of 10% extra time built in).
> The Canadian technical standard RTD 10 will give the actual requirements.
> Try http://www.tc.gc.ca/eng/railsafety/rtd10-805.htm or
> The standard doesn't discuss how the 20 seconds were determined. In 30 years
> working with crossings I never thought to inquire into the details. However
> I gained the impression it was more or less empirical, and the 20 second
> standard was effectively reverse-engineered through trial and error.
> Don Thomas
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