Route/speed signal interface-aspects?

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Route/speed signal interface-aspects?

Postby MattW » Thu Nov 19, 2015 5:46 pm

Ok, so I have yet another question about signals I hope someone can answer. How is the interface between route and speed signal territory handled? A great example of this is Stevenson, AL where the ex-Southern NS joins CSX heading to Chattanooga. The NS line which joins CSX and runs on trackage rights to Chattanooga, has a single 1 over 3 signal guarding the interlocking. Under route signaling, the best aspect would be diverging clear, under speed signaling the best aspect (at this location - medium speed switch) would be medium clear. How is this situation handled here and elsewhere? Would that signal be a speed-signal with the distant to that also being a speed-signal (so trains would get approach medium, then medium clear/approach)? Or would that still display the NS's route-signal aspect with a timetable instruction giving the speed over the switch(es) (so trains would get approach diverging then diverging clear/approach)?
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Re: Route/speed signal interface-aspects?

Postby Engineer Spike » Mon Nov 23, 2015 10:41 pm

There are lots of places where the two types of signaling come together. When I was in passenger service for BN in Chicago is one. Burlington has route signals, but it transitions to PRR speed signals coming into Union Station. I don't recall how the last Burlington signal would relay what the first Pennsy would show.

I can think of several ways this could be handled. One might be for some timetable instruction for a non conforming aspect. The last Burlington route signal may show an Approach Diverging. Knowing the possible aspects and indications of the first PRR signal is part of route familiarity. This would be how the engineer knew if the first speed signal would be a Limited, Medium, or Slow speed. Burlington used Approach, then Restricting for some equivalent of a Slow speed route.

I would have to be qualified on the location which you mentioned. My examples are just some ways which the situation could be handled. Some locations exist where nothing is 100% perfect. D&H has a siding, which has another control point about 2000' past the end of the siding. A train to be held at that next controlled point would get Advance Approach, Approach, and Stop, if routed on the main. If going via the siding it gets Medium Approach Medium, Medium Approach, and Stop. Because of the short distance between the end of the siding, and the next signal, the engineer must have hold.There is no indication which can say that you must be at Medium speed, but stop at the second signal. It is just part of knowing the characteristics.
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Re: Route/speed signal interface-aspects?

Postby ExCon90 » Tue Nov 24, 2015 3:53 pm

An interesting wrinkle about transitioning from the Burlington to the PRR coming into CUS is that on the PRR, right up until the PC merger, Medium Speed was one-half the maximum authorized speed for passenger trains, not exceeding 30 mph, so if track speed approaching CUS was less than 60, medium speed was half of that. One example was once pointed out to me on the approaches to 30th St. in Philadelphia where you could get Approach Medium on a pedestal signal and then Slow Clear on a dwarf, because passenger-train speed at that point was 30 mph. After the PC merger Medium Speed became a flat 30 mph, so presumably they had to fix that by changing it to either Approach Slow or Approach.

One location I've observed is CP COAST at Santa Clara, CA, where Caltrain from San Francisco joins the UP from Oakland, and a commute [sic] train for San Jose or Gilroy changes from eastbound under speed signaling to southbound under route signaling, and there is a wayside sign reading END SPEED SIGNALING/BEGIN ROUTE SIGNALING or words to that effect. It seems likely that they handle that as outlined by Engineer Spike, with a special instruction specifying what to expect at the interlocking. Maybe somebody who knows might see an inquiry on that in the California forum and be able to answer.
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Re: Route/speed signal interface-aspects?

Postby Engineer Spike » Tue Dec 01, 2015 9:26 pm

To be quite honest, I don't remember how the CB&Q to PRR signaling was done. I was still a trainman then, and quite new. There may have been a block signal before the first PRR interlocking.

I did have to be examined by an Amtrak rules examiner. CUS used GCOR rules, but it was almost GCOR in name only. They had so many exceptions, that it was really more like NORAC.

Speed signaling does have flaws. D&H has Medium speed signals leading to 10mph tracks. In Canada, one connection branch has Medium speed signals, but 20mph timetable speed. In these instances, the speed indicated by the signal is irrelevant.

On the other hand, there may be a controlled location where there are multiple routes. One could be Medium, while the other is Slow speed. S speed signal could indicate which one a movement was lined for. A route signal would just show that the movement was a diverging one.
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Re: Route/speed signal interface-aspects?

Postby MattW » Mon May 29, 2017 8:00 pm

Well, for the specific instance I talk about in the OP, I got confirmation over the weekend that the home signal coming off NS is indeed diverging clear/approach, while the home signal from CSX to NS is read as medium clear/approach.

I appreciate all the additional discussion this topic generated, I usually come back to thank everyone for their responses and I apologize for forgetting about this topic. :-)
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