Murph, an anaolgy would be that if you run your finger along a freshly-milled piece of lumber with the grain, you won’t get a splinter. But if you run your finger the opposite way, you almost certainly will pick up a splinter.
Think of a trailing-point move as going with the grain. The wheels push the points aside because they are facing the same direction the train is moving, so they can slide over to let the train pass. The wheels sort of wedge the points over from behind.
But, in the case of a facing-point move, the points (“splinters”) are in charge. They are non-negotiable, and the train will always go the way the points dictate, period.
“Facing point move” and “trailing point move” refer to train movement direction, not switch movement.
So, as Balt said, let’s say a train is doing a trailing point move (let’s say out of a siding and onto the main, “running through” a spring switch lined for the main), but before the whole train has cleared the spring switch, the train backs up, or a lot of slack runs out rearward; cars that had come out of the siding will now back onto the main; the problem being that those cars are coupled to the rest of the train that is still in the siding. Something has to give. Big, bad splinter happens.
Before they started putting in the manual interlockings at the end of sidings on the Mason City Sub, all the sidings had spring switches at the south end. So the normal practice would be to have the southbounds go into the hole. Once in a while the dispatcher would do things differently, putting a northbound in the siding.
Normal practice for southbounds depended on how close the northbound to met was. If it was close, the SB conductor would line into the siding and get on the engine. The NB conductor would close the switch and go. Unless there were going to meet another SB. If it wasn’t close the SB conductor would (depending on circumstances) usually line the switch back once in the clear and walk up to the head end.
SB trains left the sidings through the spring switch, so they didn’t need to restore it. Putting a NB into the siding meant possibly walking the train twice. Once to enter the siding, once to leave the siding.
Spring switches in dark territory might also have a switch point indicator for facing point moves. Depending on what they use, a green or yellow light means the switch points are firmly (no gap) against the rail. Red or Lunar means the switch needs to be tested. Stop and flop. Stop the train, line the switch reverse and normal and see that the points fit properly.
In signalled territory, the block signals fulfill the switch point indicator roll. If the points aren’t correct the circuit controller is supposed to shunt the signals, setting them red.
Hills, MN is on the BNSF Marshall subdivision that runs southwest from Willmar, MN to Sioux City, IA. Along with the Sioux City subdivision (south from Sioux City to Ashland, NE), it is unsignaled track warrant control operation with PTC.
However, these lines have an unusual feature at the siding switches called Remote Control Power Switches (RCPS). These are dispatcher-controlled power switches that physically are almost identical to a CTC power switch, but there are no controlling signals. Here’s what happens: before the dispatcher issues a track warrant over a given switch, he lines the switches for the route the train will take. In other words, he lines all of the switches within the warrant for the main line, except that if the train is supposed to clear the main line at the end of its limits, that last siding switch will be lined for the siding. The switches must be locked in the correct position for the CAD to issue the track warrant, and can’t be unlocked until the warrant is released.
This improved efficiency because only one train has to stop for a meet, and no one has to hand-line any switches. However, the system doesn’t allow the dispatcher to issue “after arrival” warrants (and indeed BNSF practice is to avoid such warrants under most circumstances). In other words, Train A and Train B can’t have warrants over the same piece of track at the same time (as they sometimes can if, for instance, the meet point is an “island” of CTC in the middle of TWC territory).
So for a hypothetical meet at Hills:
The dispatcher lines the north siding switch at Hills for the siding, then issues a warrant to southbound Train to proceed south to NSS Hills and clear the main at that point.
Northbound Train B gets a warrant to proceednorth to NSS Hills and hold the main.
Let’s assume Train A arrives before Train B. Train would go into the siding and clear it’s warrant. The dispatcher would then line NSS Hills back to the m
Interesting. On BNSF, where they have put in dispatcher controlled switches at the sidings, I believe it has been either RCPS switches in dark territory (see my previous post) or, in TWC / ABS territory, an “island” of CTC island that runs the whole length of the siding.
Do they have a lot of industries that are switched from the siding? Or do they leave cars on the sidings on a regular basis? If so I suppose I could see why they might not want to install CTC and turn it into a “controlled” siding. On a CTC siding switching requires special conversations with the dispatcher, and derails have to be interlocked with the signal system.
Did you perhaps mean to write:“if the train is supposed to clear the main line at the end of its limits, that last siding switch will NOT be lined for the mainline.”?
Personally - I view having two separate menthods of control within one territory as being dangerous - for both the train & engine crews as well as the Train Dispatcher. Both crafts can find out things the hard way as potentially can the rest
Hills, MN is on the BNSF Marshall subdivision that runs southwest from Willmar, MN to Sioux City, IA. Along with the Sioux City subdivision (south from Sioux City to Ashland, NE), it is unsignaled track warrant control operation with PTC.
However, these lines have an unusual feature at the siding switches called Remote Control Power Switches (RCPS). These are dispatcher-controlled power switches that physically are almost identical to a CTC power switch, but there are no controlling signals. Here’s what happens: before the dispatcher issues a track warrant over a given switch, he lines the switches for the route the train will take. In other words, he lines all of the switches within the warrant for the main line, except that if the train is supposed to clear the main line at the end of its limits, that last siding switch will be lined for the mainline. The switches must be locked in the correct position for the CAD to issue the track warrant, and can’t be unlocked until the warrant is released.
This improved efficiency because only one train has to stop for a meet, and no one has to hand-line any switches. However, the system doesn’t allow the dispatcher to issue “after arrival” warrants (and indeed BNSF practice is to avoid such warrants under most circumstances). In other words, Train A and Train B can’t have warrants over the same piece of track at the same time (as they sometimes can if, for instance, the meet point is an “island” of CTC in the middle of TWC territory).
So for a hypothetical meet at Hills:
The dispatcher lines the north siding switch at Hills for the siding, then issues a warrant to southbound Train to proceed south to NSS Hills and clear the main at that point.
Northbound Train B gets a warrant to proceednorth to NSS Hills and hold the main.
Let’s assume Train A arrives before Train B. Train would go into the siding and clear it’s warrant. The dispat
PTC offered a once-in-a-lifetime to put power switches in place in territory that couldn’t otherwise justify the investment, at a relatively low MARGINAL cost. In other words, if you had to put in switch point monitors and broken rail detection, the additional cost of putting a power switch was lower than it would have been on pure dark track. On the other hand, there was also pressure not to let the already enormous cost of PTC grow out-of-hand either. I’m not surprised that different roads came up with different approaches.
The UP system you describe does more to aid train movement than the RCPS system I described (if your rules allow the DS to issue “After Arrival” warrants for meets at those sidings). It also costs more, so that’s a trade-off someone made.
BUT what I DON’T understand is why they wouldn’t call the track in between the switches CTC, or in other words why they require a warrant on the main line between switches. With control points (pardon me, “manual interlockings”) at each end, with (I assume) signals at one end acting as distant signals for the other end, and a track circuit in between for broken rail protection, you have 95-99.9% of the equipment you would need to just have a CTC island. The only difference would be that, for a CTC island, any mainline switches between the siding switcheswould need electric locks in addition to t
Elk Creek and Carnes sidings in the time table have manual interlockings at each end. They also show as having ABS between the switches, with no signals beyond. Part of the subdivision has ABS, the rest is dark as of the time table issue. I didn’t look to see if there have been changes since it’s issue.
On the Mason City Sub, it’s TWC/ABS. They can issue after arrival warrants there because it’s signalled territory. I think they can’t, at least they stopped that practice a few years ago, and I haven’t kept up on dark TWC territory. I don’t know if the ABS island allows them to issue the after warrant.
Carnes is the siding they had that collision many years ago because of the way they were issueing warrants. A train was tied down on the main between the switches. IIRC, another train held two warrants. Both were “work betweens”, one work between A and Carnes, the other work between Carnes and Z. Both warrants gave authority to the siding switches, but not authority on the main between the switches. The crew didn’t catch that they needed to use the siding. The resulting collision spilled onto a crew van waiting to pick up a crew on another train. After this, they curtailled the use of “work between” warrants when a train didn’t actually need the work between authority.