Western Railroad Discussion > Signals on the UP

I have a couple questions on the UP signal system. My daily commute takes me along the UP Altoona sub for about 10 miles. About 2 years ago they upgraded the system to led signals, when they went active they were lit on approach only. That lasted about 6-8 months at which time they went to lit all the time. That lasted about a year at which time they went back to approach lit but only on one signal. Now that one signal that was approach lit has went back to lit all the time. Why would they keep changing the way they are lit?  The second question is this; we have a sand plant outside of town that has 2 control points about 1 mile apart. The main line signals at the plant are normally red except when a through train is coming. The signal before is steady yellow and the signal before that is flashing yellow. Why not just have them green all the time and change them for sand plant traffic? Thanks.

I can answer part two of your question.  These aren't control points, which would be absolute signals, but intermediate signals in advance of the control point at the sand plant.  The dispatcher must clear the signal at the sand plant for each train because it is an absolute signal.  The two preceding signals show that the upcoming control point is going to have a stop indication, hence the flashing yellow (advanced approach) follwed by a yellow (approach).  Once the dispatcher clears the absolute for the main line, both those intermediates will turn green.  Absolute signals are generally only set when a train is routed through them, otherwise they show stop.  If they showed clear all the time, then when the dispatcher wanted to route something via the alternate path he would have to wait for the signal to time out before the routing could take effect.  If the signal is red in both directions, no time out is necessary to clear one route or the other.

the 2 signals prior to the CP are approach signals telling rhe engineer he's approaching an absolute signal ...

the advance approach signal indication tells the engineer that he must be prepared to stop at the second signal ...

the approach signal indication tells the engineer that he must be prepared to stop at that next signal ...

the 2 approach signal indications are triggered by whatever signal indication is displayed on the absolute signal ... so for whatever reason the absolute signal indication was displaying less than clear indication for the advance approach and approach signal indications to be dispalyed ...