Wallers Ash loops

[swt_passenger]

One of the aims of the 'strategic freight network' improvements in CP4 was to extend the operational length of Wallers Ash loops (just west of Micheldever) to cater for 775m freight trains.

If I'm correct, they seem to have just recently completed the changes at this location, basically by re-siting the signals for exit from the loops further towards the relevant junction in normal direction of travel. In practical terms two new signal posts have been installed trackside, and the previous normal direction 'loop' signals sited on the main gantries over the four track layout have been removed.

I think in a previous discussion it was pointed out that there's a signalling design convention that requires signals on two parallel lines to normally be at the same chainage for sighting purposes, but that doesn't seem to have been carried on in this case. Was this a firm requirement, or just guidance, as presumably moving the main running signals to match would have made the job much more involved.

 

[Muzer]

Presumably this has affected the overlap in some way? I don't know what it is or was at this location - did it used to foul the main line, and does it now?

 

[Timothy Turtle]

I think in a previous discussion it was pointed out that there's a signalling design convention that requires signals on two parallel lines to normally be at the same chainage for sighting purposes, but that doesn't seem to have been carried on in this case. Was this a firm requirement, or just guidance, as presumably moving the main running signals to match would have made the job much more involved.

As far as I know, there is no absolute requirement for signals to be parallel, although it is considered to be good practise as it reduces the risk of drivers reading the wrong signal for the line they are on. If there is a good reason for not having the signals parallel (as at Wallers Ash) it would be up to the signal sighting committee to have the final say.

 

[swt_passenger]

Presumably this has affected the overlap in some way? I don't know what it is or was at this location - did it used to foul the main line, and does it now?

Taking the down loop as an example, it is about 1500 yards long (measuring the parallel part of the track only). The distance from the start of the loop to the down direction gantry is over 800 yards, and from that gantry to the end of the loop was about 600 yards. It seems from observation the signal is now about 300 yards further west which must provide a similarly increased loop length, with at least 300 yards of overlap remaining.

If you use Google maps or similar you'll see the two gantries basically divide the loop location into three parts, so in each direction you previously had about ⅔ of the length as a loop, and ⅓ as overlap.

--- old post above --- --- new post below ---

As far as I know, there is no absolute requirement for signals to be parallel, although it is considered to be good practise as it reduces the risk of drivers reading the wrong signal for the line they are on...

Thanks, I thought I'd read something along those lines before. Of course the situation here is straight and level, so I guess the view the driver gets may now have the two signals at significantly different heights as the main is on a gantry and the loop signals are somewhat lower, and to the left.

 

[SomerWinton]

I can't understand why, though, that the loops were built on a high embankment, when around 500m down the line southwards towards Wallers Ash tunnel. There is ample land to provide four tracks at near enough grade where the up and down lines diverge from each other horizontally and leave quite a space between them.

Perhaps the loops could be extended to this location in the future if longer lengths are required?

 

[swt_passenger]

I can't understand why, though, that the loops were built on a high embankment, when around 500m down the line southwards towards Wallers Ash tunnel. There is ample land to provide four tracks at near enough grade where the up and down lines diverge from each other horizontally and leave quite a space between them.

Perhaps the loops could be extended to this location in the future if longer lengths are required?

The loops were originally much longer. I was told quite a few years ago now they were shortened to the present length following an under bridge or embankment failure. That failure is also something to do with why the up and down lines are spread apart between the tunnel and the loop entry. A book I have describes the loops as 1¼ miles long as far back as 1965, so that suggests about 6-700 yards has been removed.

Welcome to the forum by the way - I see this is your first post...

 

[Tio Terry]

There is a recommendation that signals on adjacent lies be located at the same chainage. However, with the agreement of the Signal Siting Chairman and the members of the SS Committee this can be varied. In the case of Wallers Ash it's possible to get a full overlap with the changed positions and this was agreed by the SS committee.

 

[MarkyT]

There is a recommendation that signals on adjacent lies be located at the same chainage. However, with the agreement of the Signal Siting Chairman and the members of the SS Committee this can be varied. In the case of Wallers Ash it's possible to get a full overlap with the changed positions and this was agreed by the SS committee.

Also in this case from the description of the work in the discussion above the signal on the higher speed through line is the one likely to be seen first on approach, so reading through to the wrong one on the loop is highly unlikely. In the event that a main line train was brought to a stand whilst something was pulling out of the loop, the train would have been warned early by previous adverse aspects, and the train in the loop could be blocking the view anyway. The loop signal will be sighted for the loop and may be a shorter range variant on the basis that any trains approaching it will be running at the the lower loop speed, preparing to stop.

A maximum length train can take ages to clear the main line into a tight loop that is only just capable of taking the train, as the tail is still crawling through the turnout whilst the loco is creeping up to the signal, so any extension can have significant benefits, and moving signals like this can be very cost effective. Note an overlap, which is provided by default on a freight line today can be significantly shorter for a slow loop approach than on a parallel fast mainline. A throw off trap point, with no overlap has been unacceptable for such loop applications for many years, but an overrun spur leading to a friction buffer stop can form an acceptable overlap.

 

[Bill EWS]

I remember the reduction in length of the Up & Down Loops. Apparently at the south end there is an underbridge that affected the weight going over it. It was reduced to two tracks going over it instead of four plus the turnouts.

It was a mistake rducng the loops in the first place nd it is nice that they have exteneded them once again.

 

[swt_passenger]

Just to follow up the estimate I made of the relative position of the signals in post #4 above, I recently checked using a stopwatch and the down direction loop exit signal is almost exactly half way between the original position on the gantry, and the end of the loop, so that adds to the evidence that there's still about 300 yds of overlap.

--- old post above --- --- new post below ---

I remember the reduction in length of the Up & Down Loops. Apparently at the south end there is an underbridge that affected the weight going over it. It was reduced to two tracks going over it instead of four plus the turnouts...

Thanks for that confirmation Bill. Do you remember if under the original setup the signalling was positioned to allow for two trains to be held in the loops?