Preston PSB signal PN14 near Euxton

[Springs Branch]

A couple of recent threads on distant signals & banner repeaters reminded me of one of the great mysteries of the WCML from my youth (at least, mysterious in my mind) . . .

Why was a green aspect not available on signal PN14 ?

Here's the background:
- The attachment shows historic signalling arrangements around the Balshaw Lane Jn. / Euxton Jn. area of the WCML.
- The diagram is extracted from a BR Signalling Notice issued in 1972 during commissioning of Preston PSB.
- Where the WCML transitions from four tracks to two at Balshaw Lane Jn, the junction is protected by controlled signal PN9 on the Up Slow, with PN14 the automatic signal in rear acting as the junction's "up slow inner distant". It's still the same today.
- Euxton Balshaw Lane station is now located between those two signals, but is not shown - the station was still closed at the time.
- PN14 is marked on this diagram (and others I've seen) as not having a green aspect available - on an otherwise conventional 4-aspect TCB route.

My questions are:

• Does the current LED version of signal PN14 now display a green? (or is it still capable of only R, Y, YY ?)
• Why was PN14 set up this way back in 1972?
• Were there other examples of this '4-aspect with no green' elsewhere?

I had assumed there was some sort of approach control at the time applied to trains approaching PN9 and Balshaw Lane Junction on the Up Slow.
However, if this were true, it doesn't make sense to have Double Yellow available on PN14. Surely PN14 could only ever display either Red or Single Yellow?

At present the Sectional Appendix shows the Slow Lines with a 75 mph speed limit, and 75 mph through the points at Balshaw Lane Jn., so presumably no need for any approach control these days.

Any ideas why this one-off anomaly existed here?

 

[The Planner]

Its all 4 aspects now.

 

[Annetts key]

My questions are:

• Were there other examples of this '4-aspect with no green' elsewhere?

On Western at Chipping Sodbury, where the reversible signalling on the up line (down the up) comes to an end, because the speed over the crossover is slow, the "junction" signal is approach released (approach controlled) from red. Hence the reversible signals leading up to it can show yellow/red and double yellow/single yellow/red only.

I had assumed there was some sort of approach control at the time applied to trains approaching PN9 and Balshaw Lane Junction on the Up Slow.
However, if this were true, it doesn't make sense to have Double Yellow available on PN14. Surely PN14 could only ever display either Red or Single Yellow?

The junction signal may have been approach released from yellow.

 

[james_the_xv]

Were there other examples of this '4-aspect with no green' elsewhere?

Not a specific example but approaching terminus stations in 4 aspect areas you'll can have signals that only display R, Y, YY.

 

[furnessvale]

Not a specific example but approaching terminus stations in 4 aspect areas you'll can have signals that only display R, Y, YY.

It would seem to be common sense to me that if you have insufficient block sections before the stop blocks, you cannot display the green aspect, or even the YY as you get closer.

 

[Earle Grey]

• Why was PN14 set up this way back in 1972?

I'd say it was down to junction design more than anything - the attached maps from 2003 (I suspect nothing much has happened in between), shows linespeed drop from 75mph to 50mph just before the junction. There is/was a warning just before Balshaw Lane Station to show this.

By PN14 not being able to display a green aspect a driver will always be slowing down for PN9 regardless of what PN9 displayed. If memory serves I think the junction was upgraded to 75mph around 2014/5 (?)

 

[edwin_m]

This is an excerpt from the report into the 1972 accident at Eltham Well Hall, when a train derailed on a 20mph curve after a long unrestricted section: https://www.railwaysarchive.co.uk/documents/DoE_Eltham1972.pdf

This would have been around the time the Preston signalling was being designed, although the report wasn't published until 1973. I wonder if the designers had in mind the risk that something similar could happen there, a less severe speed restriction but also a risk of head-on collision at the junction.

 

[Springs Branch]

This is an excerpt from the report into the 1972 accident at Eltham Well Hall, when a train derailed on a 20mph curve after a long unrestricted section:

This would have been around the time the Preston signalling was being designed, although the report wasn't published until 1973. I wonder if the designers had in mind the risk that something similar could happen there, a less severe speed restriction but also a risk of head-on collision at the junction.

That's a plausible explanation given the circumstances & timing. The Eltham accident occurred on 11 June 1972, while the Preston PSB Signalling Notice diagram was issued in October 1972 for new arrangements commissioned on 22/23 October 1972.

Possibly the original design and installation of PN14 had been for a conventional 4-aspect signal, which was modified at a late stage, post Eltham.

Not far south, on the Up Slow approaching Golborne Junction was a very analogous situation to PN14. This area was also re-signalled in late 1972 as part of the same northern WCML modernisation / electrification scheme.

The 4-track WCML from Wigan converged into two tracks over a 50 mph-restricted junction, just before the Parkside lines took off to the left. Here, the equivalent 4-aspect signal WN141 - which acted as the nominal Up Slow Inner Distant for the junction - seemed to be equipped to show all four aspects.

 

[driver9000]

When I first learned south of Preston about 18 years ago Balshaw Lane Junction was 50mph down from 75mph on the Up Slow (it was actually 50 in both directions). I was told PN14 couldn't show a green aspect as a way to control the speed of trains approaching the junction. When junction was remodelled around 2013 and speeds raised to 75mph throughout the green aspect at PN14 was enabled. I don't know if Golborne Junction had the same set up at the time but today trains can be signalled through the junction on greens coming off the Up Slow.

A similar set up exists departing Preston in the Up direction from platform 1 where the signal also can't show a green aspect.