signal questions 3

[NW Mailing List]

On 6/3/2015 4:49 AM, NW Mailing List wrote:
>
> At first glance, 
> http://www.railpictures.net/viewphoto.php?id=472679&nseq=319 looks 
> like a recipe for disaster atIngleside. But what is really going on 
> here? I believe the camera is looking into the aspects that an 
> Eastbound movement would observe and it shows clear for both mains. 
> Because of the long exposure, we can also see reflections of the 
> Westbound aspects, and they are stop and ?approach? Why would you ever 
> want opposing movements to both see “go ahead” aspects for the same 
> track at the same point?
>

As a bystander, you can view signal conditions like this in the absence 
of traffic that a train crew would never see.

> Let's dig a little deeper. The Eastbound signals are a control point 
> (note the single lights under the top arm) for the next block.
>

Generally:

All signals indicate the track conditions ahead, a lined route, or idle, 
in that order.

All signals are either Stop and Stay or Stop and Proceed.

All signals are either controlled or automatic.

All controlled signals are Stop and Stay.

All Stop and Proceed signals are automatic.

However,

some Stop and Stay signals are automatic.

Signals are labeled "Stop and Stay" or "Stop and Proceed" based on their 
most restrictive indication and this distinction must be indicated by a 
permanent means, thus, the lack of a number plate indicates a Stop and 
Stay signal. There is no such ready indication to distinguish controlled 
signals from automatics beyond the constraints listed above. Ultimately, 
one must know the territory to be sure. As Joe mentioned, the Ingleside 
eastward signals are Stop and Stay automatics because the safe stopping 
distance ahead overruns the sight distance due to a combination of 
descending grade and blind curves (the reverse of a Grade Signal 
application).

> However, the Westbound signals are intermediates (automatic). It 
> appears that the dispatcher has set routes Eastward on both mains, 
> thus the clear aspects. One of the Westbound intermediates is showing 
> stop and proceed, as I would have expected, but why does the other 
> show approach?
>

This has to do with using the idle indications as a starting point to 
decipher what is going on, but they can vary on automatic signals 
depending on the application. Again, one must know the territory to be 
sure. Normally (if there is such a thing), idle automatics display Clear 
or Approach if ahead of a controlled signal. However, with double mains, 
they often display their most restrictive aspect on the reverse main. 
This is not the case at Ingleside nor at Elkhorn Tunnel.

> Under the “tumble down” operational scenario, I was under the 
> impression that when a route was established between control points 
> for a movement in one direction, all the intermediates between the two 
> control points were immediately dropped to their most resticting 
> aspect, i.e. stop and proceed. My question is: why does the one 
> intermediate show approach, and why is this safe? Another example of 
> this seemingly unsafe behaviour is shown in 
> http://www.railpictures.net/viewphoto.php?id=510649&nseq=1 at Willowton.
>
> Thanks, Jim Cochran
>

Jimmy covers this in his excellent illustration. What I would term a 
"controlled block" between two controlled signals in the same direction, 
must be clear for the signals to be able to reset. Like an interlocking, 
this prevents a conflicting route from being lined. The tricky part can 
be the movement against the current of traffic, depending on the situation.

Grant Carpenter


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