A blog devoted to explaining the ins and outs of North American railroad signaling, past, present and future. This blog seeks to preserve through photo documentation the great diversity and technical ingenuity of 20th century signaling and interlocking hardware and technology. Related topics cover interlocking towers and railroad communications infrastructure.
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Saturday, December 31, 2016
Caught on Camera: Approach Restricting
The Approach Restricting signal indication has a bit of a bad reputation in the land of speed signaling east of the Mississippi. Typically, the signal progression in both the NORAC and CSX codes are Approach -> Restricting with the idea being that since Restricting could be displayed with an obstruction 5 feet inside the signal, there is no benefit to preparing the engineer to do anything other than stop. Yes, NORAC does have an "Approach Restricting" rule, but it's basically a re-branded distant Approach or PRR Caution signal that doesn't really capture the spirit of approaching a signal in block signaled territory and finding the next signal displaying a Restricting indication.
Calling this "Approach Restricting" is an insult to "Approach Restricting"
So the real Approach Restricting is found in route signaled territory both in the west and on the Southern. Now I know that you are thinking that "Restricting" implies a speed, but the rationale behind Approach Restricting is much more apparent in a route signaled context. Below is the true meaning of Approach Restricting, caught on camera.
Y/L Approach Restricting leads yo...
R/Y Restricting for a route into a siding.
The traditional use of Approach Restricting was as a route indication to alert trains that they had been routed into a non-circuited (Restricted speed) siding. This was popular out west because there Single Track with Passing Siding was the predominant form of rail line. Once CTC started being installed it was logical to distinguish a movement into a signaled siding (Approach Diverging) from a non-signaled track (Approach Restricting) from some sort of regular Stop or Stop and Proceed signal (Approach). However, as speed signaling has started to gain traction on western roads, signal engineers and consultants have started employing it a wider variety of situations.
Ok, tk1 has a route lined at the next interlocking and tk 2 does not. Is this distinction really going to make a different here?
For example on the CN Waukesha Sub (METRA North Central line), Approach Restricting was widely applied as a capacity improvement, although as eastern railroaders pointed out, it's unclear how much one actually gains from this unless one is bending the rules of being able to stop within 1/2 vision. Approach Restricting (and Medium Approach Restricting) has also showed up on the hyper speed signaled Caltrain line, right along side Approach Slow.
Y/*R* Approach Restricting
This of course brings up the alternate Approach Restricting aspect, Y/*R*, which of course has become popular as *R* took over for Lunar for Restricting (since using 4-lamp monster heads is just wacky *cough*CSX*couch*). Since many two headed distant signals use placeholder Reds, this has made all of them a potential location to employ Approach Restricting. In fact, when the aforementioned CN Waukesha Sub was re-re-signaled, Y/*R* Approach Restricting came in to replace the lunars. You can see an example of "speed" style Approach Restricting on the following video montage of flashing signals on the Waukesha Sub (cut to time code 00:23).
Well I hope this sheds some light into the past, present and future of the Approach Restricting indication.
Cool post about a very interesting aspect. In addition to before a Restricting aspect, Union Pacific also uses Approach Restricting in multi-aspect signaling for short blocks, e.g. sequences like Advance Approach > Approach Restricting > Approach > Stop. In this case, the Approach Restricting is used like Approach Slow is sometimes used on a speed-signaled road.
The Approach Restrictings on the CN Waukesha Sub are useful to tell crews that the next signal is lined for them. For example, southbound freight trains often hold just north of the intermediate signals at Lake Villa (shown in the photo above). Seeing the Y/L come in alerts them that they have a lineup at the following signal (Round Lake control point) and can start pulling (and usually by the time they reach the signal, they have an upgraded aspect). It’s a little more information for train handling, avoiding blocking road crossings, and so on.
Another note on CN's signal practices. On its ex-DMIR trackage, if a train is lined up to follow another past an absolute signal, it will show Restricting rather than Stop, and then Approach Restricting, often requiring a second head with just a red light. I've never seen a train follow that closely, but in beavy traffic it might just be useful. Then again, CN has some interesting ideas in their route-signal system...
Cool post about a very interesting aspect. In addition to before a Restricting aspect, Union Pacific also uses Approach Restricting in multi-aspect signaling for short blocks, e.g. sequences like Advance Approach > Approach Restricting > Approach > Stop. In this case, the Approach Restricting is used like Approach Slow is sometimes used on a speed-signaled road.
ReplyDeleteThe Approach Restrictings on the CN Waukesha Sub are useful to tell crews that the next signal is lined for them. For example, southbound freight trains often hold just north of the intermediate signals at Lake Villa (shown in the photo above). Seeing the Y/L come in alerts them that they have a lineup at the following signal (Round Lake control point) and can start pulling (and usually by the time they reach the signal, they have an upgraded aspect). It’s a little more information for train handling, avoiding blocking road crossings, and so on.
Another note on CN's signal practices. On its ex-DMIR trackage, if a train is lined up to follow another past an absolute signal, it will show Restricting rather than Stop, and then Approach Restricting, often requiring a second head with just a red light. I've never seen a train follow that closely, but in beavy traffic it might just be useful. Then again, CN has some interesting ideas in their route-signal system...
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