I've seen signals that told a train that they had to limit speed until the entire train passed a switch. How does the engineer know when it has passed the switch since the trains vary in length, no one is in a caboose to tell them (unless the 'caboose' is a manned pusher/helper) and there are no cameras on the rear of the train? Guess, GPS, magic?
Magic.
The opinions expressed here represent my own and not those of my employer, any other railroad, company, or person.
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Perry BabinI've seen signals that told a train that they had to limit speed until the entire train passed a switch. How does the engineer know when it has passed the switch since the trains vary in length, no one is in a caboose to tell them (unless the 'caboose' is a manned pusher/helper) and there are no cameras on the rear of the train? Guess, GPS, magic?
The End of Train Devices being used by the Class 1 carriers have a distance counter built into their electronics. Engineer has the ability to Zero the counter on demand. From the Train Documents in the crew's possession it is known the length of the train. Bingo, Bango, Bongo the Engineer knows when the train has moved a train length and the rear is now clear of the restriction.
Some Defect Detectors 'may' also report a train length when broadcasting the 'Defect Report' for a train passing over a DD. Many have been changed to only report the number of axles the DD has had pass over it, instead of length.
Never too old to have a happy childhood!
I didn't know that the EoTD could do anything other than monitor air pressure.
How can the DD know length? Articulated cars would make axle count fairly inaccurate due to single trucks/bogies being used for 2 car bodies.
The EOT/SBU has nothing to do with distance measuring. Most do have GPS, but this is so the railroad can find them if they get lost in the ditch.
Locomotives do have a distance counter built into them, on newer units it's in the computer and on older ones it will be part of the HOT/IDU module. They aren't always perfectly accurate, if your speedometer is off the counter probably will be too.
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-an Articulate Malcontent
Perry BabinI didn't know that the EoTD could do anything other than monitor air pressure. How can the DD know length? Articulated cars would make axle count fairly inaccurate due to single trucks/bogies being used for 2 car bodies.
Axle count is Axle count - not car count. Train documents contain car data including contents, weight, individual car length and number of axles. The car data is drawn from the UMLER data base that contains virtually all aspects and dimensions of every rail car being used in Interchange Service within the North American continent (ie. US, Mexico, Canada) as well as the carriers own car and train movement data base for the loading and gross weight of the loaded car (load weight from the waybill data + the empty car weight from UMLER.
The following video shows defect detector reporting in a model railroad setting. Real railroad equipment is more sophisticated but is doing the same kind of job and making almost identical kinds of 'defect reports'.
BaltACDFrom the Train Documents in the crew's possession it is known the length of the train. Bingo, Bango, Bongo the Engineer knows when the train has moved a train length and the rear is now clear of the restriction.
I have never summoned up the nerve to ask the engine crew what they're going to do to get around this situation.
Overmod BaltACD From the Train Documents in the crew's possession it is known the length of the train. Bingo, Bango, Bongo the Engineer knows when the train has moved a train length and the rear is now clear of the restriction. Except that "the length of the train" if it contains a large percentage of cushion underframes may be hundreds of feet more 'stretched' than 'bunched'. I have seen multiple instances of trains nearly the length of White Siding in east Memphis come to a stop with 2-3 cars still foul of the switch when the power comes to rest at the foul zone at the other end. Presumably he used more air than dynamic to slow the train, and many of the underframes remained 'stretched' as the cars came to a stop... I have never summoned up the nerve to ask the engine crew what they're going to do to get around this situation.
BaltACD From the Train Documents in the crew's possession it is known the length of the train. Bingo, Bango, Bongo the Engineer knows when the train has moved a train length and the rear is now clear of the restriction.
Except that "the length of the train" if it contains a large percentage of cushion underframes may be hundreds of feet more 'stretched' than 'bunched'. I have seen multiple instances of trains nearly the length of White Siding in east Memphis come to a stop with 2-3 cars still foul of the switch when the power comes to rest at the foul zone at the other end. Presumably he used more air than dynamic to slow the train, and many of the underframes remained 'stretched' as the cars came to a stop...
Hope the other train is short enough to fit between switches. If not it is usually the Dispatcher's fault for setting up an oversiding meet, or perhaps at least one of the crews or the clerk centre did not calculate the train length properly.
This happens occasionally over the years. On a busy mainline with lots of double track and long sidings it is usually easiest to have one train back up to a location where they can both meet. But sometimes you end up performing the dreaded saw-by.
It is usually preferred to keep the train stretched out if your tail end is barely going to clear something. This means there will be less roll-back of slack when you release the brakes. If the tail end rolls backward and runs through a switch or stop signal it is treated just like the same rule violation committed while moving forward. It is actually quite common for us to request 'rollback protection' from the RTC before releasing the brakes in such a situation, while the rules do not allow the RTC to authorize a otherwise blind reverse movement on signal indication alone or even tell a crew that they have a permissive signal behind them, they are allowed to say the coded phrases "rollback protection is in place" or "the signal is now on request" after it shows clear on the CTC panel. Now if your tail end rolls back through the light it will not be a stop signal violation.
In situations where rollback protection is requested and the RTC is not able to give a permissive signal indication behind a train the crew will have to copy a written work authority, but the end result is the same (no unauthorized movement or block occupancy).
That is one of the reasons that Dispatchers would inquire of crews what kind of length figure the DD's were giving the trains - to compare it with the Train Document length that was applied to the Train Sheet for the train.
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