New Chiltern Railways' timetable promises faster times from May 2011

[whole diary]

[paul7575]

Here's a detail question about the signalling layout at Aynho Jn then, albeit late!  Today I saw one of these preliminary route indicators (PRIs) active - the one just south of Kings Sutton, displaying a straight up indication which I expect is what you'd get on a service headed from Banbury towards Oxford.  [If the drawing is an accurate depiction I assume 90 degrees left is towards Bicester and 45 degrees right is the crossover to the down flyover line?]

Could industry insider possibly explain the rationale behind having PRIs and flashing yellows in the same area?  I suspect this is a relatively new idea?  Doesn't the flashing yellow sequence already do the job of route indication for Bicester?

Paul

[readytostart]

I think it's because signal BS104 controls access to the Up Bicester, the flyover and the goods loop, each with a different approach speed. By relying on just the flashing sequence and the route indicator on the signal BS104 would have to be approached assuming the slowest route was set until you get sight of the actual signal indication.

[eightf48544]

Interesting comment re different approach speeds.

DB^» (Deutsche Bahn - German State Railway - about) have solved the problem with their new Ks siganls, by telling the driver the speed to run in the points zone after the siganl and if necessary also giving an advanced warning of the speed to run after the next signal.

However, it doesn't tell him where he's going.

[paul7575]

So in the sequence of decision making - a driver seeing the flashing yellow sequence knows he's OK for the Bicester route, and the following PRI are really just belt and braces - ie they aren't giving him any new info.

If however there is no flashing sequence the PRI becomes more important, because it is now giving advance info for a different choice of two routes.

Am I right in assuming there is no PRI indication for the up goods loop - so would that route only be indicated by the feather on BS104 - or will the PRI have a 'blank' indication?

Paul

[readytostart]

Am I right in assuming there is no PRI indication for the up goods loop - so would that route only be indicated by the feather on BS104 - or will the PRI have a 'blank' indication?

The speed into the loop is only 15mph so I would assume that BS104 would be kept at danger until the train was moving fairly slowly. I expect that as the signal was at danger no route is officially set so the PRI would be blank.

[IndustryInsider]

So in the sequence of decision making - a driver seeing the flashing yellow sequence knows he's OK for the Bicester route, and the following PRI are really just belt and braces - ie they aren't giving him any new info.

If however there is no flashing sequence the PRI becomes more important, because it is now giving advance info for a different choice of two routes.

Yes, that's pretty much it.  I might be repeating a little of what has already been quoted, but as I understand it:

The PRI signals do indeed just exist to stop drivers taking the wrong route as green aspects will now be displayed when the route is set for the Up Main or the Up Bicester.  The flashing yellows will be displayed if the train is going to cross over onto the Down Bicester, and if the train is to be routed into the Up Goods Loop it will get a green at BS106, a single yellow at BS104R and then an approach controlled Position Light signal complete with No.1 Junction indicator (with the main aspect staying red) at BS104.  As for the PRI's they will remain blank if a train is going to be routed through the Up Goods Loop as a proceed aspect at BS104 has yet to be displayed - this would also be the case should the train be stopped at BS104 for any reason.

[ChrisB]

Chiltern are releasing their May11 TT very soon - sort ofclose to the current one, but the stopping patterns more match that now due on September 12.....the same date that the cOtswold get their new one.

[paul7575]

So in the sequence of decision making - a driver seeing the flashing yellow sequence knows he's OK for the Bicester route, and the following PRI are really just belt and braces - ie they aren't giving him any new info.

If however there is no flashing sequence the PRI becomes more important, because it is now giving advance info for a different choice of two routes.

Yes, that's pretty much it.  I might be repeating a little of what has already been quoted, but as I understand it:

The PRI signals do indeed just exist to stop drivers taking the wrong route as green aspects will now be displayed when the route is set for the Up Main or the Up Bicester.  The flashing yellows will be displayed if the train is going to cross over onto the Down Bicester, and if the train is to be routed into the Up Goods Loop it will get a green at BS106, a single yellow at BS104R and then an approach controlled Position Light signal complete with No.1 Junction indicator (with the main aspect staying red) at BS104.  As for the PRI's they will remain blank if a train is going to be routed through the Up Goods Loop as a proceed aspect at BS104 has yet to be displayed - this would also be the case should the train be stopped at BS104 for any reason.

Thanks, all makes sense now - although I'd actually misread things    and thought the flashing aspects indicated the Up Bicester route, but they actually deal with the relatively unusual situation of using the Down Bicester route.  Hence the two 'normal choices' are covered by the two PRIs - because (and this is quite significant) they are both 90 mph routes, and they can both be taken at normal line speed.

 

[SandTEngineer]

....... and if the train is to be routed into the Up Goods Loop it will get a green at BS106, a single yellow at BS104R and then an approach controlled Position Light signal complete with No.1 Junction indicator (with the main aspect staying red) at BS104.  .

I would doubt that.  Current rules do not permit a position light signal associated with a main aspect to be displayed with a junction indicator.  A miniature route indicator must be provided unless this signal is over 10 years old in which case you are correct

[IndustryInsider]

Yep, thanks for spotting that error, SandTEngineer - I didn't know the rules had changed!

I've re-checked the signalling notice and should a train be routed into the Up Goods Loop at BS104 it will receive one of two indications; either an approach controlled main aspect (single yellow I suspect) with a No 1. Junction Indicator, or the main aspect will stay red and all that will be displayed is the two white lights of the position light signal - for when permissive freight procedures are being followed.  Everything else in my original post is correct.

I should point out that although the alterations in the signalling notice have taken effect, there's still a lot of work to do, with one of the 40mph crossover connections to install and the connection off of the Down Bicester will need a little work doing to it.  The whole area is TSR^▸ (Temporary Speed Restriction)'d with a 30/50 at present - I'll let you know when the job has been finished.