Western Railroad Discussion > UP Signal Question...

Hello TO.com land,

I have a question for the UP signal folks here on TO.com.

Last friday morning to work, I saw the intermediate at MP 2.9 on the Graham Line of the Portland Subdivision. It had a green block for e/b movements and a yellow for w/b movements. They were displaying those aspects at the same time. I know I have seen this in the past. I saw it again this morning.

What does that mean?? What would cause it to display proceed movements at the same time??


TIA,

SP8100

SP8100 Wrote:
-------------------------------------------------------
> Last friday morning to work, I saw the
> intermediate at MP 2.9 on the Graham Line of the
> Portland Subdivision. It had a green block for
> e/b movements and a yellow for w/b movements.
> They were displaying those aspects at the same
> time. I know I have seen this in the past. I saw
> it again this morning.
>
> What does that mean?? What would cause it to
> display proceed movements at the same time??

Some intermediates display aspects based on track occupy and the condition of signals at Control Points. It will only display this particular set of aspects if there were no trains between the control points on both sides of this intermediate AND the dispatcher hasn't cleared a train into that track segment. Since the next signal westbound is most likely a control point, the signal is yellow for westbound and there must be several clear blocks east for the eastbound to be green. As soon as a train entered the block on either side of this intermediate, the signal in the opposite direction will tumble down to red.

What kind of territory is this? ABS, CTC, ??

EtoinShrdlu Wrote:
-------------------------------------------------------
> What kind of territory is this? ABS, CTC, ??

CTC as far as I know..


SP8100

In all the CTC installations I've ever experienced, intermediates show a permissive indication in one direction and a stop (and proceed) in the other because of the way the "tumbledown" works. Assuming the DS hasn't cleared any controlled signals, the permissive indications will appear in the last used direction of traffic between the controlled signals; in the opposite direction they will all be red.

With ABS, on the other hand, it's normal for "intermediates" ("block signals", actually) to show permissive indications in both directions, unless there is a train approaching from one direction or the other, because in ABS directionality between sidings is determined by traffic load (approaching trains).

Thus, I suspect this Graham line is ABS, particularly if it's low density traffic route. CTC is expensive to install, and if traffic levels can't justify the investment . . . . The subdivision's timetable schedule page will give a definitive answer.

On the UP's Kansas Sub, which is 2 main track CTC, I have seen signals display yellow for both directions when nothing is lined through. The signal I am thinking about is the only intermediate between absolute signals. So, it can happen even in CTC.

It's called poor man's CTC. CTC islands with the equivalent of ABS in between. The BNSF Seligman Sub. is this way. You can have a "clear" in both directions
unless a train is approaching from the other direction, then the train itself causes the "tumble down". The Gallup Sub. has "real" or "full" CTC, where as the
dispatcher will line the route, causing the "tumble down".



Edited 1 time(s). Last edit at 11/13/12 12:54 by qnyla.

The Graham Line is CTC ACS. There aren't any controlled signals between East Portland and Troutdale.