Points Questions

Bald Rick said:

Not exactly high speed though.

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furnessvale said:

True. The UK seems to have an aversion to slips full stop.

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At about 09:45 hrs on 22 March 2009, train 2N50, the 09:17 hrs from Alloa to Glasgow Queen Street, formed by a three-car class 170 diesel multiple unit,
traversed Greenhill Upper Junction (figure 2) at 64 mph (103 km/h). One of the point ends, designated 125C, forming part of a set of switch diamonds, was in the incorrect position and the train trailed through them forcing them across to the correct position and damaging the mechanism as a result.
...
The permissible speed for trains crossing the junction to or from the Larbert direction is 70 mph (113 km/h); the permissible speed for trains on the Edinburgh and Glasgow line is 100 mph (161 km/h).

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coppercapped said:

To your point No. 2.

One of the constraints in the design of turnouts and junctions on curves, such as that at Southcote Junction, is the degree of super-elevation ('cant') on the curve of the main routes. In this case the speed limit on the 'main' route - that from Reading West towards Newbury, is 60mph and the tracks are tilted towards the inside of the curve accordingly, see the illustration in this Wiki page. Each track is canted separately which means that the 'high' rail on the Up Newbury line line will be higher that the 'low' rail on the Down line. This means that any track from the Basingstoke direction a diamond crossing in the down Newbury line will have to be twisted so there are no 'steps' in the rails where the two lines cross and this will, of necessity, mean an even more severe speed restriction of the Basingstoke route.

By trying to place the turnouts on straighter lengths of track the significance of the super-elevation issue is reduced and having a series of single lead points enables the civil engineer to match track geometries better. In the dim and distant days when Southcote Junction was a double junction with a diamond crossing the speed limit towards Basingstoke was (IIRC) 40mph (and may have been less - I'm trying to remember what it was like 40 years ago and more) and that on the Newbury route was 50mph. So the present layout is a definite improvement.

As to your point about about time loss, in the particular instance of Southcote Junction this is minimal. On the Newbury route from Reading West the speed limit is 60mph from the northern end of the platforms to past Southcote Junction and the speed limits on the turnouts to the Basingstoke line are 50mph southbound and 45mph northbound. So southbound trains have to lose 10mph and northbound ones can't be running at more than 60mph anyway as they join the main line - a 15mph difference. The container trains, running roughly hourly in each direction, are limited to 30mph between Oxford Road Junction (at Reading West) and Reading West Junction on the Relief lines to Didcot - in view of their weight the southbound trains won't have changed speed much between Reading West and Southcote Junction so the effect of the speeds at Southcote Junction on their running times will be very small and the northbound trains will be braking for the 30mph turnout at Oxford road Junction. Trains calling at Reading West will not be running at line speed so the trains which are most affected are the one or two per hour Cross Country services which are non-stop between Reading and Basingstoke.

All engineering is a compromise between several competing factors. In this case I would suggest that the engineers made the correct call.

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markymark2000 said:

Thank you. This is very detailed and helps a lot.

The times I have noticed the speed decrease most was towards Basingstoke on the GWR service and they definitely lost more than 10mph (I would say probably about 50 down to around 30 until just over the junction and then sped back up again). It could have been a TSR or something but it happened a few times so I thought it was more permanent. Northbound seems faster but less comfortable with the way the points are.

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coppercapped said:

According to the June 2019 issue of the Wessex Route Sectional Appendix (can be downloaded from Network Rail's website as a pdf) there is a permanent 45mph speed limit in the Basingstoke direction from 37 miles 76 chains to 38 miles 8 chains, this is just south of Southcote Junction. The limit then increases to 75mph until the outskirts of Basingstoke.

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civ-eng-jim said:

The approach control to junctions is sometimes a bit rudimentary (Thinking along the lines of approach release) reducing the approaching train to a speed that's far lower than the capability of the turnout.

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Bald Rick said:

Those PSRs are for the junction. The junction isn’t shown in layout form in the KSW Sectional Appendix as it is ‘off patch’.

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coppercapped said:

In which case I'm confused...!

The Western and Wales Sectional Appendix shows Southcote Junction at 37 miles 62 chains; going south towards Basingstoke that's 14 chains before the boundary with Wessex. There is no 45mph limit shown on the southbound line in the WW SA, this limit is only seen in the KSW SA and it starts at the boundary. The PSRs for the junction in the WW SA are 50mph to Basingstoke southbound and 45mph from Basingstoke northbound.

I'll have to go to have a look!

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Bald Rick said:

It’s 50 through the junction itself, then 45 round the curve beyond it. Possibly to do with signal sighting of BE501.

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MarkyT said:

I suspect the turnout speed was chosen to avoid the need for any approach release in the signalling.

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Bald Rick said:

Sorry I misread your post.

The junction is 37m62c
The route boundary is 37m76c

It’s 50 through the junction itself, then 45 round the curve beyond it. Possibly to do with signal sighting of BE501.

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