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Distance of train from signaled crossing


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#1 LookingGlassTie

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Posted 07 December 2017 - 07:47 PM

Curious question:

 

I've watched many YouTube videos of Amtrak trains passing through signaled crossings.  Why is it that at some crossings, the lights start flashing, the bells start ringing and the arms come down well before the train gets there, while at other crossings, those things occur just barely prior to the train's arrival?  From what I've seen, it doesn't seem to be dependent on the speed of the train.  

 

What's the explanation for that?  Thanks!


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#2 Alexandria Nick

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Posted 07 December 2017 - 08:34 PM

The quick and dirty answer is that the detectors are set out a specific distance to activate the signals at least 20 seconds before a train would arrive at the crossing, if said train was traveling at the highest allowed track speed.  If the train is traveling slower or the signals are tuned differently, then you'll have a longer wait.  There's ways they can tune the signals to activate differently based on speed, but you'll always get at least 20 seconds, because that's a Federal law.



#3 Just-Thinking-51

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Posted 07 December 2017 - 08:49 PM

The arms are to close 20 seconds to a maximum 30 seconds before a train arrives.

However there are dumb crossing and there are smart crossing.

A dumb crossing is set up with the max speed of the track and a sensor will trigger the crossing lights and gates. However if the speed of train is below track speed the sensor will not adjust the timing, so a longer than 30 seconds of the gates down may occur.

A smart crosssing has a computer that will determine the speed of the train and active the crossing gates and flasher so they will be down 20 to 30 seconds before the train approaches.

This is the modern system for any new crossings. However you can find the older system on Branch lines, and short lines.

Of course if a train is too close (fowls) to the gates, the crossing will remain active and down even if the train has stop.

#4 Ziv

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Posted 10 December 2017 - 11:06 AM

I think the 20 second rule may be counterproductive, though it probably does eliminate a certain proportion of Darwin Award winners.

If people see that the arms come down and then they have to wait 20 to 30 seconds day after day for the train to arrive, they are much more likely to try to drive around the gates, even if they really know that it is a stupid thing to do. People can do incredibly stupid things when they are under time pressure. If they knew that the train would be arriving 10 to 15 seconds behind the gate dropping, they wouldn't even dream of trying to beat the train through the intersection. The difference between waiting 10 to 20 seconds vs. waiting 20 to 30 seconds seems huge when you are late to pick up your kids or late for work.



#5 Seaboard92

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Posted 10 December 2017 - 07:30 PM

When I spent time on a signal crew I learned quite a bit about signaling. The crossings we had one included three crossings that were daxed together meaning that if one activated they all were activated on the same circuit. Each box on the inside has a countdown clock that is at 99 and as the train approaches it goes down to 0. Our crossing the main four lane Main Street signal would activate once the gates had closed at church st, and shortly after Carolina Blvd would activate.

All based on the speed of the train. Now on a shortline railroad I've worked with the engineer could punch the crossing ID into the radio and lower the gates much like a signal maintained. But that was a crossing used by one train one day a month.
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#6 ehbowen

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Posted 10 December 2017 - 08:16 PM

I think the 20 second rule may be counterproductive, though it probably does eliminate a certain proportion of Darwin Award winners.

If people see that the arms come down and then they have to wait 20 to 30 seconds day after day for the train to arrive, they are much more likely to try to drive around the gates, even if they really know that it is a stupid thing to do. People can do incredibly stupid things when they are under time pressure. If they knew that the train would be arriving 10 to 15 seconds behind the gate dropping, they wouldn't even dream of trying to beat the train through the intersection. The difference between waiting 10 to 20 seconds vs. waiting 20 to 30 seconds seems huge when you are late to pick up your kids or late for work.

 

Ziv, I think you could make it 3 seconds and some people would STILL try to beat the train.


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#7 Ziv

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Posted 10 December 2017 - 08:22 PM

ehb, you are right about some people trying to beat the train even if the wait was just 3 seconds. But I think that the amount of people trying it would be MUCH less and that a 10 to 20 second wait would probably be safer for more people in the long run than a longer wait. Sometimes we over reach when we try to do a good thing, and the results are less than optimal. Good intentions don't equal good results.

 

 

I think the 20 second rule may be counterproductive, though it probably does eliminate a certain proportion of Darwin Award winners.

If people see that the arms come down and then they have to wait 20 to 30 seconds day after day for the train to arrive, they are much more likely to try to drive around the gates, even if they really know that it is a stupid thing to do. People can do incredibly stupid things when they are under time pressure. If they knew that the train would be arriving 10 to 15 seconds behind the gate dropping, they wouldn't even dream of trying to beat the train through the intersection. The difference between waiting 10 to 20 seconds vs. waiting 20 to 30 seconds seems huge when you are late to pick up your kids or late for work.

 

Ziv, I think you could make it 3 seconds and some people would STILL try to beat the train.

 



#8 Thirdrail7

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Posted 13 December 2017 - 09:04 PM

 

ehb, you are right about some people trying to beat the train even if the wait was just 3 seconds. But I think that the amount of people trying it would be MUCH less and that a 10 to 20 second wait would probably be safer for more people in the long run than a longer wait. Sometimes we over reach when we try to do a good thing, and the results are less than optimal. Good intentions don't equal good results.

 

 

I think the 20 second rule may be counterproductive, though it probably does eliminate a certain proportion of Darwin Award winners.

If people see that the arms come down and then they have to wait 20 to 30 seconds day after day for the train to arrive, they are much more likely to try to drive around the gates, even if they really know that it is a stupid thing to do. People can do incredibly stupid things when they are under time pressure. If they knew that the train would be arriving 10 to 15 seconds behind the gate dropping, they wouldn't even dream of trying to beat the train through the intersection. The difference between waiting 10 to 20 seconds vs. waiting 20 to 30 seconds seems huge when you are late to pick up your kids or late for work.

 

Ziv, I think you could make it 3 seconds and some people would STILL try to beat the train.

 

 

 

 

If that is your logic, maybe we should save the money, eliminate the grade crossing gates and lights altogether and let people go it alone. If you don't have 20 seconds, 30 seconds or 2 minutes to save your life, then you timed your day wrong and we'll just see you on the other side.


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#9 neroden

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Posted 13 December 2017 - 09:19 PM

Maybe you could replace the gates with iron spikes and flamethrowers. Leave the bells and lights, but *guarantee* that anyone who tries to beat the train will be killed, even if they *do* beat the train. And make sure they don't delay the train.

Edited by neroden, 13 December 2017 - 09:19 PM.

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#10 LookingGlassTie

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Posted 13 December 2017 - 09:29 PM

Thanks for the replies!

 

A follow-up question:  do some crossings also have sensors in the road near the tracks so that if a train is close enough, any motor vehicles in the vicinity will trigger the arms to come down?  In addition to the switches along the tracks?


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#11 me_little_me

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Posted 13 December 2017 - 09:39 PM

Concrete barriers that come up from the pavement.



#12 Ryan

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Posted 13 December 2017 - 10:01 PM


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#13 SarahZ

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Posted 13 December 2017 - 10:13 PM

 

Idiots.


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#14 Hotblack Desiato

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Posted 13 December 2017 - 11:41 PM

Thanks for the replies!

 

A follow-up question:  do some crossings also have sensors in the road near the tracks so that if a train is close enough, any motor vehicles in the vicinity will trigger the arms to come down?  In addition to the switches along the tracks?

 

Not sure what the point of this would be.  Why would you want an automobile to trigger the crossing arms?



#15 Seaboard92

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Posted 14 December 2017 - 12:54 AM

Thanks for the replies!
 
A follow-up question:  do some crossings also have sensors in the road near the tracks so that if a train is close enough, any motor vehicles in the vicinity will trigger the arms to come down?  In addition to the switches along the tracks?


Only if whatever vehicle shunts the track circuit. The crossings I've worked with there is an electric charge that is going out from the crossing on each side of the island. The island is the actual crossing itself. As the train approaches the crossing it shunts the circuit and activates a relay that activates the crossing. Now if the train doesn't reach the island in time the crossing will then deactivate.

And that's a very basic definition. Now there are crossings that can determine the speed of the train and compute when to activate.
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