Speeding up the South West Main line

[Palmerston]

If the South West Main line (or some of it), plus the West of England line had overhead electric lines, how much if any of the line could potentially be increased to 125 mph? The distances to Weymouth and Exeter are not dissimilar to the Midland Main Line, with Southampton to London seeing more journeys than anywhere north of Bedford on the MML.

 

[SynthD]

Assuming improved ground conditions, over bridges and level crossings are solved, it’s largely about the minimum radius in certain sections like Farnham.

Currently the only 100mph section is Byfleet to north Southampton, minus Basingstoke. Farnborough to Basingstoke (~21km) is the straightest part of that, but it may only permit 110mph. If that were possible, the next question might be is it worth the increased cost and possible reduced throughput?

 

[Zomboid]

The Farnborough to Basingstoke section alignment would probably be good for 200mph, it's completely straight. Most of the line is pretty straight, and the first level crossing is in Southampton just before the 15mph curve so that's not an issue. Ground conditions are another thing, no idea about that.

Most of the Basingstoke to Salisbury section is pretty straight too, and no level crossings there either. Past there the stations are too frequent to be worth much line speed enhancement, unless the idea is to replace the GWML for the fast Devon to London trains.

 

[Bald Rick]

There are getting on for 100 different factors to consider when raising the permitted speed of a line, of which the horizontal alignment (curvature) is but one.

 

[Bletchleyite]

It's always struck me how absolutely dead straight a fair part of the SWML is, so presumably it'd just be a case of changing third rail to OHLE, new stock and fettling the track a bit, assuming what you wanted was 125 rather than proper high speed?

 

[brad465]

You'd need more 4-track between Worting Jct and Southampton to cater for the freight and faster passenger services. The area though I'd be looking more for improvements is Southampton-Bournemouth, which is slower (max 90) while still having high traffic. This would though require remodelling over the River Test, among other changes.

 

[TastyMaltesers]

Since you're including the line to Exeter in this query, I think there's a lot more issues at play with that section than just the line speed...

 

[Bald Rick]

It's always struck me how absolutely dead straight a fair part of the SWML is, so presumably it'd just be a case of changing third rail to OHLE, new stock and fettling the track a bit, assuming what you wanted was 125 rather than proper high speed?

It would be complete resignalling, regauging, every bridge and embankment assessed (many of which would need work), much of the track completely replaced, many of the safe access walkways moved, and so on. Then it woudl be quite a large business change - for example the maintenance strategy would be completely rewritten, and the timetable would (naturally) need to be recast. Then you’d have to buy some new trains and all that goes with them.

 

[cle]

Also west of Salisbury, trains stop a lot. West of Basingstoke even. So the savings may not be worth it, and you might be better starting with raising the lower speeds up. But yes a service running non-stop Basingstoke-Salisbury for instance, might benefit from a faster section (and more trains through that part than the extremity).

The Basingstoke-Reading line, which is not on this route but certainly feeds it in times of closures, and on Sundays - would benefit far more from new signalling and line speeds, re the amount of trains (and stock/service profile, eg XC)

 

[devon_belle]

I have been told stories of slamdoor units getting up to 125 mph on the SWML. Presumably without permission... it was a different time. These days I doubt the electricity supply would be happy with a Desiro attempting the same.

When 442s were being tested were they run at 110 mph on any stretches?

 

[quantinghome]

Also west of Salisbury, trains stop a lot. West of Basingstoke even. So the savings may not be worth it, and you might be better starting with raising the lower speeds up.

100 times this. There's no point whatsoever increasing the linespeed when the maximum distance between station stops west of Basingstoke is less than 19 miles, and in many cases only a few miles. Higher line speeds would only be worth it if you run a non-stop service. In which case... just run a non-stop service at the current linespeed. That will save more time than expensive upgrades. But it would be counterproductive - the point of the SWML isn't to get to Exeter as quickly as possible; it's to connect the towns along the way, and that means stopping, and that means there's no point having a high linespeed.

But yes a service running non-stop Basingstoke-Salisbury for instance, might benefit from a faster section (and more trains through that part than the extremity).

Even then it's only 32 miles between the speed-limiting junctions. You wouldn't save much.

 

[cle]

100 times this. There's no point whatsoever increasing the linespeed when the maximum distance between station stops west of Basingstoke is less than 19 miles, and in many cases only a few miles. Higher line speeds would only be worth it if you run a non-stop service. In which case... just run a non-stop service at the current linespeed. That will save more time than expensive upgrades. But it would be counterproductive - the point of the SWML isn't to get to Exeter as quickly as possible; it's to connect the towns along the way, and that means stopping, and that means there's no point having a high linespeed.


Even then it's only 32 miles between the speed-limiting junctions. You wouldn't save much.

Perhaps not, but with sometimes 2 fasts per hour (and calls for more eg WRATH / Paddington in the long term, or more local service) - - - - as well as 2tph stoppers (which could be sped up and have quicker working patterns - also with better acceleration) - it could make a difference to the overall operation.

 

[brad465]

Maybe have a "Salisbury Express", a service that runs non-stop from Waterloo-Salisbury, then carries onto Exeter with a suitable calling pattern for demand and single track allowances (that would hopefully see more double track reinstated).

I'd make it the current Exeter service, with the Salisbury terminator retaining its calling pattern and Gillingham/Yeovil extensions, but increased to all day, then an hourly service between Basingstoke and Salisbury that has 2-hourly extension to Yeovil Pen Mill/Jct via Westbury, with 2-hourly split portions off Exeter services on top as happens now to an extent.

Given that a trunk road runs near-parallel to this line (A303 and M3), potential demand for more and/or faster services will exist.

 

[cle]

Maybe have a "Salisbury Express", a service that runs non-stop from Waterloo-Salisbury, then carries onto Exeter with a suitable calling pattern for demand and single track allowances (that would hopefully see more double track reinstated).

I'd make it the current Exeter service, with the Salisbury terminator retaining its calling pattern and Gillingham/Yeovil extensions, but increased to all day, then an hourly service between Basingstoke and Salisbury that has 2-hourly extension to Yeovil Pen Mill/Jct via Westbury, with 2-hourly split portions off Exeter services on top as happens now to an extent.

Given that a trunk road runs near-parallel to this line (A303 and M3), potential demand for more and/or faster services will exist.

This isn't that different to today in principle - you probably want Andover calls which has hit 1m users but non-stop Waterloo to Andover might be interesting.

Your hourly Basingstoke - Salisbury with extensions, should reasonably start at Reading - bringing all that that does.

Andover would still have 2tph to Basingstoke in your plan.