Didcot-Swindon "getting full" - possible capacity improvements?

brad465 · 7 Jun 2026

The latest RAIL edition has an item on Network Rail warning there is only one spare path every 2 hours along this stretch of the mainline and that it's close to being declared "congested". What would be the best options for alleviating this?

The article mentions they've tried to get more electric traction on freight, which can accelerate out of loops faster, though this doesn't do much. Other ideas floated include extending existing loops and signalling enhancements. IIRC this section is mostly 3-aspect; what difference would 4-aspect make?

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The Planner · 7 Jun 2026

brad465 said:
The latest RAIL edition has an item on Network Rail warning there is only one spare path every 2 hours along this stretch of the mainline and that it's close to being declared "congested". What would be the best options for alleviating this?

The article mentions they've tried to get more electric traction on freight, which can accelerate out of loops faster, though this doesn't do much. Other ideas floated include extending existing loops and signalling enhancements. IIRC this section is mostly 3-aspect; what difference would 4-aspect make?

4 aspect won't make a difference unless the overall sections are reduced. It will need longer loops/4 tracking.

brad465 · 7 Jun 2026

The Planner said:
4 aspect won't make a difference unless the overall sections are reduced. It will need longer loops/4 tracking.

I would have thought if plans to 4-aspect the section were ever pursued, shorter sections would be part of this anyway. The best section to 4-track I think would be west of Didcot-Wantage, as that combines two separate sets of loops into one, however this means dealing with Steventon, so I wouldn't be surprised if 4-tracking almost all the way from Wantage to Swindon is easier.

BrianW · 7 Jun 2026

The latest RAIL edition has an item on Network Rail warning there is only one spare path every 2 hours along this stretch of the mainline and that it's close to being declared "congested". What would be the best options for alleviating this?

The article mentions they've tried to get more electric traction on freight, which can accelerate out of loops faster, though this doesn't do much. Other ideas floated include extending existing loops and signalling enhancements. IIRC this section is mostly 3-aspect; what difference would 4-aspect make?
[/QUOTE]

Easy- remove the recently added every two hours GWR 5-car Class 800 Bristol- Bath-Chippenham-Swindon-Oxford.

Or make it a 9 or 10-car ...

Or use the path for a London train.

cle · 7 Jun 2026

BrianW said:
The latest RAIL edition has an item on Network Rail warning there is only one spare path every 2 hours along this stretch of the mainline and that it's close to being declared "congested". What would be the best options for alleviating this?

The article mentions they've tried to get more electric traction on freight, which can accelerate out of loops faster, though this doesn't do much. Other ideas floated include extending existing loops and signalling enhancements. IIRC this section is mostly 3-aspect; what difference would 4-aspect make?

Easy- remove the recently added every two hours GWR 5-car Class 800 Bristol- Bath-Chippenham-Swindon-Oxford.

Or make it a 9 or 10-car ...

Or use the path for a London train.

For what? To be an empty path. What this says to me is that Oxford - Bristol should go hourly. And then this is fully utilized. There are no other growth plans for it so why leave excess capacity?

Lines should be run as close as workable possible to max capacity, obviously.

The Planner · 7 Jun 2026

brad465 said:
I would have thought if plans to 4-aspect the section were ever pursued, shorter sections would be part of this anyway. The best section to 4-track I think would be west of Didcot-Wantage, as that combines two separate sets of loops into one, however this means dealing with Steventon, so I wouldn't be surprised if 4-tracking almost all the way from Wantage to Swindon is easier.

Depends if can you reduce the spacings and still keep the 125mph. Even then, you still might not create a headway reduction.

quantinghome · 7 Jun 2026

A look at Realtimetrains suggests there are 5-6 trains per hour in each direction on this stretch. That doesn't really scream congested to me given they are pretty much all intercities.

The Ham · 7 Jun 2026

BrianW said:
Easy- remove the recently added every two hours GWR 5-car Class 800 Bristol- Bath-Chippenham-Swindon-Oxford.

Or make it a 9 or 10-car ...

Or use the path for a London train.

Are there any paths into London which could be paired with it?

If London capacity was the issue, it's likely to be preferable to do something like get fixed length 10 coach battery trains and pass the 80x's to XC (might also need some more wires towards Bath/Bristol).

The Planner · 8 Jun 2026

quantinghome said:
A look at Realtimetrains suggests there are 5-6 trains per hour in each direction on this stretch. That doesn't really scream congested to me given they are pretty much all intercities.

Try sticking a freight in that is starting from a stand at Challow and has to get through the 11 miles to Highworth with a 125mph IET up your backside.

The exile · 8 Jun 2026

cle said:
Lines should be run as close as workable possible to max capacity, obviously.

Not obvious at all - use all the capacity and the minute something goes wrong you’ve got almost no hope of recovery.

The Planner · 8 Jun 2026

The exile said:
Not obvious at all - use all the capacity and the minute something goes wrong you’ve got almost no hope of recovery.

Indeed, we need to get away from filling every piece of white space to earn money from it.

brad465 · 8 Jun 2026

Was this section 4-track over a much longer stretch in the past before being rationalised? That might help determine how easy future quadrupling is to carry out.

Zomboid · 8 Jun 2026

The bridges suggest not, though I remember seeing a signal in place for a loop that no longer existed (down direction. I think) somewhere along there.

The exile · 8 Jun 2026

The Planner said:
Indeed, we need to get away from filling every piece of white space to earn money from it.

Go to many of the countries praised for reliable railway services (or indeed ones that used to be) and one of the things you'll notice is what to British eyes look like enormous, "underused" stations which sometimes even enable "1 platform per route - 1 route per platform"

mr_jrt · 8 Jun 2026

brad465 said:
Was this section 4-track over a much longer stretch in the past before being rationalised? That might help determine how easy future quadrupling is to carry out.

Recalled having this discussion in the past, and have the info (with links to maps) in my old post:

Great Western Electrification Progress

There is the potential for 140mph operation but the DfT will still have to decide, when all the required elements are in place, notably once ETCS cab signalling is operational, whether it wants to foot the bills that 140mph will bring, in terms of extra energy use and train maintenance bills...

www.railforums.co.uk

Mikey C · 8 Jun 2026

I assume any reopening of the station at Wantage and Grove would be dependant on finding ways to increase capacity on this stretch?

brad465 · 8 Jun 2026

mr_jrt said:
Recalled having this discussion in the past, and have the info (with links to maps) in my old post:

Great Western Electrification Progress

There is the potential for 140mph operation but the DfT will still have to decide, when all the required elements are in place, notably once ETCS cab signalling is operational, whether it wants to foot the bills that 140mph will bring, in terms of extra energy use and train maintenance bills...

www.railforums.co.uk

Thanks for sharing this.

Mikey C said:
I assume any reopening of the station at Wantage and Grove would be dependant on finding ways to increase capacity on this stretch?

Depending on pathing times, this station may assist in capacity. If the Oxford-Bristol service calls at the station on the relief loops, one or two fast services could overtake. Making the loops longer though would still help, especially when considering the need to path freight.

cle · 8 Jun 2026

Yes loops would help for freight - there are no slows but Oxford-Bristol seems to be the pick for scooping future station calls up given that many would indeed travel to Oxford. But suggesting we cut a hard-won service that has barely begun is short sighted. Maybe we look towards more freight interventions (cancelling unused paths, re-timing it to be overnight only, longer dynamic loops (which could also potentially have platforms at key locations) - vs cutting. It's always a race to the bottom and X vs Y in this country.

alistairlees · 8 Jun 2026

What is the current pattern of services that makes it "full"? There is no statement of what this is, or why it makes it "full".

zwk500 · 8 Jun 2026

brad465 said:
Depending on pathing times, this station may assist in capacity. If the Oxford-Bristol service calls at the station on the relief loops, one or two fast services could overtake.

Only if there's not a freight stuck waiting for a gap. It's just as likely (maybe even more likely) that trying to call at Wantage Road on the Relief lines will mean needing to take freight out.

brad465 said:
Making the loops longer though would still help, especially when considering the need to path freight.

ideally you'd connect the 4 track at Foxhall Jn (Didcot) to Wantage Road with grade-separation to take the Down relief from alongside the Up Relief to alongside the Down Main. However that's only going to do so much and really for freight you would be looking at providing a loop somewhere between Bourton and Uffington Crossovers (i.e. halfway between Swindon and Challow). But the closer you get towards Bourton the more bridges there are to contend with, and you'd still struggle to avoid freight coming to a stand completely.

The exile · 8 Jun 2026

alistairlees said:
What is the current pattern of services that makes it "full"? There is no statement of what this is, or why it makes it "full".

The off-peak passenger service will be 2 Bristols, 2 South Wales, 1 Cheltenham and the Oxford - Bristol. Other than any differences caused by stopping / not stopping at Didcot, or crawling round the West Curve there, those presumably all have comparable pathing requirements. Looking at the current hour there appear to be two down freight paths, one of which has run today. (I assume that the Banbury and appleford - Whatley paths 6C50 and 6C48, both scheduled to pass Wantage Road at 13.40 are "either / or / neither", not "and")

alistairlees · 8 Jun 2026

The exile said:
The off-peak passenger service will be 2 Bristols, 2 South Wales, 1 Cheltenham and the Oxford - Bristol. Other than any differences caused by stopping / not stopping at Didcot, or crawling round the West Curve there, those presumably all have comparable pathing requirements. Looking at the current hour there appear to be two down freight paths, one of which has run today. (I assume that the Banbury and appleford - Whatley paths 6C50 and 6C48, both scheduled to pass Wantage Road at 13.40 are "either / or / neither", not "and")

Thanks. That's very helpful. I took a quick look at RealTimeTrains for services in the hour from 12:00 to 1259 on Monday 15th June:

DID - SWI
12:06 - 12:20 (to Bristol TM)
12:11 - 12:27 (to Cheltenham)
12:24 - 12:38 (to Carmarthen)
12:38 - 12:59 (to Bristol TM) (6.5 minutes pathing allowance)
12:53 - 13:08 (to Cardif Central)

Every two hours there is the Oxford - Bristol TM which is (using Foxhall Junction instead of Didcot Parkway)
xx:16 - xx:33

Then there are 2 or 3 freights per hour.

So on average about 7 trains per hour, leading to congestion; presumably it's the spacing and the (differing) performance characteristics, as well as some conflicting moves at Foxhall Junction, that lead to this?

quantinghome · 8 Jun 2026

The Planner said:
Try sticking a freight in that is starting from a stand at Challow and has to get through the 11 miles to Highworth with a 125mph IET up your backside.

I'd rather not...

OK, so it's the freight / intercity differential wot does it. Four-tracking it is then.

Where is the demand for more services though? Intercities? More freight? Reinstate local stations and have a stopping service? Also, given most traffic carries straight on at Swindon, you'd probably want to extend four tracks to Wootton Bassett Jn. I'm guessing there's not a great deal of capacity for extra services further east on the GWML either.

Dr Hoo · 8 Jun 2026

cle said:
Yes loops would help for freight - there are no slows but Oxford-Bristol seems to be the pick for scooping future station calls up given that many would indeed travel to Oxford. But suggesting we cut a hard-won service that has barely begun is short sighted. Maybe we look towards more freight interventions (cancelling unused paths, re-timing it to be overnight only, longer dynamic loops (which could also potentially have platforms at key locations) - vs cutting. It's always a race to the bottom and X vs Y in this country.

Given the government’s target of 75% freight growth by 2050, a key ingredient of which is likely to be large amounts of scrap traffic from the South East to the new electric arc furnaces of Port Talbot, any idea of cancelling unused paths rather than protecting and probably expanding them is ‘unwise’.
Similarly, an overnight-only freight model would totally destroy sustainable freight asset utilisation, quite apart from not meeting customers’ requirements. It would also be unachievable alongside the increasing maintenance needs of an even busier corridor hammered by 125mph passenger trains and heavy axle load freight.

Bald Rick · 8 Jun 2026

alistairlees said:
What is the current pattern of services that makes it "full"? There is no statement of what this is, or why it makes it "full".

It’s the current service, plus the Bristol - Oxford going hourly, plus the Lumo proposals (some of which have access rights, some are in the decision process), plus freight.

”Full” might not necessarily mean no more space on the train graph, it might mean issues with level crossing risk where additonal servcies tip the balance.

The exile · 9 Jun 2026

Bald Rick said:
It’s the current service, plus the Bristol - Oxford going hourly, plus the Lumo proposals (some of which have access rights, some are in the decision process), plus freight.

”Full” might not necessarily mean no more space on the train graph, it might mean issues with level crossing risk where additonal servcies tip the balance.

I would expect it would also include, in the medium term, an extra stop on the Bristol - Oxfords (and possibly the Cardiffs) at Grove / Wantage Parkway.

Bald Rick · 9 Jun 2026

The exile said:
I would expect it would also include, in the medium term, an extra stop on the Bristol - Oxfords (and possibly the Cardiffs) at Grove / Wantage Parkway.

It doesn’t.

geoffk · 9 Jun 2026

Bald Rick said:
It’s the current service, plus the Bristol - Oxford going hourly, plus the Lumo proposals (some of which have access rights, some are in the decision process), plus freight.

Did Network Rail warn the ORR about future congestion before access rights were given to Lumo (and what level of service has been approved)?

brad465 · 10 Jun 2026

Bald Rick said:
It’s the current service, plus the Bristol - Oxford going hourly, plus the Lumo proposals (some of which have access rights, some are in the decision process), plus freight.

”Full” might not necessarily mean no more space on the train graph, it might mean issues with level crossing risk where additonal servcies tip the balance.

This would not surprise me, given the line speed at the key LC between Swindon and Royal Wootton-Bassett is being reduced to enable the hourly Bristol-Oxford to go ahead. There may not be much capacity potential in this, but closing Stocks Lane LC, then adjusting the OHLE to reinstate 125mph through Steventon would I think help, both as trains clear a signal block faster and that's one crossing that extra services could cause further safety problems if still operational.

fishwomp · 10 Jun 2026

alistairlees said:
Thanks. That's very helpful. I took a quick look at RealTimeTrains for services in the hour from 12:00 to 1259 on Monday 15th June:

DID - SWI
12:06 - 12:20 (to Bristol TM)
12:11 - 12:27 (to Cheltenham)
12:24 - 12:38 (to Carmarthen)
12:38 - 12:59 (to Bristol TM) (6.5 minutes pathing allowance)
12:53 - 13:08 (to Cardif Central)

Every two hours there is the Oxford - Bristol TM which is (using Foxhall Junction instead of Didcot Parkway)
xx:16 - xx:33

Then there are 2 or 3 freights per hour.

So on average about 7 trains per hour, leading to congestion; presumably it's the spacing and the (differing) performance characteristics, as well as some conflicting moves at Foxhall Junction, that lead to this?

In 12.00 to 13.00 - _west_ bound there was _one_ freight today. Between 13:00 and 18:00 there were only three _in total_ westbound - and eastbound there were none.

There may be that many _paths_ for freights, but a heck of a lot are 'runs as required' slots (some workings are overlapped with other as required workings), that are rarely used.

Didcot-Swindon "getting full" - possible capacity improvements?

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