GC London Extension as a High speed line

[mike57]

I know a lot has written and discussed about this route, my question is a simple one, had the route survived (Nottingham southwards), what speeds could have been acheived assuming the route remained within its original boundary.

It looks to be fairly straight on the map.

You can electrify it, relay the track, resignal, remove the stations with island platforms, and create links at Rugby and Leicester but otherwise have to stay with railway boundaries.

Would it support 125mph? More? Some of it, none of it? I realise the original section over Met tracks wouldn't be suitable for high speed running, but you then have the GWR GC Joint line into London, which still exists today and looks to be more twisty.

 

[A0]

I know a lot has written and discussed about this route, my question is a simple one, had the route survived (Nottingham southwards), what speeds could have been acheived assuming the route remained within its original boundary.

It looks to be fairly straight on the map.

You can electrify it, relay the track, resignal, remove the stations with island platforms, and create links at Rugby and Leicester but otherwise have to stay with railway boundaries.

Would it support 125mph? More? Some of it, none of it? I realise the original section over Met tracks wouldn't be suitable for high speed running, but you then have the GWR GC Joint line into London, which still exists today and looks to be more twisty.

I suspect it probably could have been made to support 125mph running given it's been achieved with the older ECML, WCML and Midland Mainline in parts.

Between Aylesbury and Sheffield, it was fairly gentle in curvature terms - the big thing would probably have been the island platforms which would probably have needed to be rebuilt to have outside platforms. Inevitably some bridges would have needed raising to accommodate OHLE but that's been the case with the electrification of every other mainline in the UK.

You also had the link down to the GW/GC joint through Ashendon - I suspect Ashendon Junction might have continued to be speed limited and south of there, you can see from the Chiltern use of the line what's possible. The bigger issue would probably have been capacity - it was a 2 track railway with limited passing places, which restricts Chiltern to this day.

 

[etr221]

My understanding is that the GC London extension (including GW&GC joint) was built as a high standard main line, so as good as any, and better than most: the exception was those bits of older lines incorporated, i.e. Met south of Quainton Road, and Wycombe Railway between High Wycombe and Princes Risborough. So with the exception of the last mentioned, I would suggest it would been easy to upgrade to 125mph continuous from Northolt Jn northwards (not so sure about further south); with higher speeds possible for much of the line, with more effort

 

[zwk500]

A table on this wiki article: https://en.wikipedia.org/wiki/Minimum_railway_curve_radius gives a minimum radius for 230kph/130mph of 1800m, with 160mm Cant.

The GC was apparently built to a curve radius of 1 Mile, or 1600m, so the suggestion of 125mph would seem to be feasible for much of the route - but you'd either have to demolish island platforms or put PSRs on them, as the clearances wouldn't be big enough. Some stations may be feasible to have 125mph loops put around them, but you need the track to be straight at the pointwork as you don't want any cant at points.

From comparing the WCML and MML to the GCR route on a map, I'd suggest that the section from London to Aylesbury would be limited to 110mph max for non-tilting trains, and only getting to 125mph from Aylesbury northwards. For context - the ECML doesn't go to 125mph until just south of Stevenage.

 

[A0]

From comparing the WCML and MML to the GCR route on a map, I'd suggest that the section from London to Aylesbury would be limited to 110mph max for non-tilting trains, and only getting to 125mph from Aylesbury northwards. For context - the ECML doesn't go to 125mph until just south of Stevenage.

Basically another 10 miles - Kings X to Stevenage is 27 miles, Marylebone to Aylesbury is 38.

I'd have thought the GC / GW joint might have been easier to increase speed on as it had been designed as a quicker line where the Aylesbury via the Met wasn't.

 

[30907]

A table on this wiki article: https://en.wikipedia.org/wiki/Minimum_railway_curve_radius gives a minimum radius for 230kph/130mph of 1800m, with 160mm Cant.

The GC was apparently built to a curve radius of 1 Mile, or 1600m, so the suggestion of 125mph would seem to be feasible for much of the route - but you'd either have to demolish island platforms or put PSRs on them, as the clearances wouldn't be big enough. Some stations may be feasible to have 125mph loops put around them, but you need the track to be straight at the pointwork as you don't want any cant at points.

From comparing the WCML and MML to the GCR route on a map, I'd suggest that the section from London to Aylesbury would be limited to 110mph max for non-tilting trains, and only getting to 125mph from Aylesbury northwards. For context - the ECML doesn't go to 125mph until just south of Stevenage.

I think you would choose the GW/GC route rather than the Met, and then you could manage high speed from Risborough to Nottingham (and you could perhaps have quadrupled Northolt Jn-Beaconsfield to get a decent speed there if not 125.
Through High Wycombe and on to P Risborough would be restrictive.

 

[zwk500]

I think you would choose the GW/GC route rather than the Met, and then you could manage high speed from Risborough to Nottingham (and you could perhaps have quadrupled Northolt Jn-Beaconsfield to get a decent speed there if not 125.
Through High Wycombe and on to P Risborough would be restrictive.

I was looking at both routes into London. Looking on Open Railway Map they are both quite severely curved until Aylesbury. Risborough-Aylesbury is not exactly straight and only a short way before the curves at either end, making 100mph+ running on that section fairly pointless. From Neasden to Princes Risborough is 100mph (with PSRs in places) today, according to ORM, and the Aylesbury-Risborough line 40mph.

125mph from Aylesbury would still compare well to the MML (125mph from Luton) and ECML (125mph from Knebworth). ORM doesn't do differential speeds but I think the WCML starts 125mph running a little closer to London than those 2. The GWML starts 125mph at Acton (the closest of the classic lines), thanks to Mr Brunel's billiard table.

 

[30907]

I was looking at both routes into London. Looking on Open Railway Map they are both quite severely curved until Aylesbury. Risborough-Aylesbury is not exactly straight and only a short way before the curves at either end, making 100mph+ running on that section fairly pointless. From Neasden to Princes Risborough is 100mph (with PSRs in places) today, according to ORM, and the Aylesbury-Risborough line 40mph.

Indeed, but that was never part of either GC route - trains via High W diverged from the GW/Chiltern route further out at Ashendon Jn and ran to Grendon Underwood Jn

 

[zwk500]

Indeed, but that was never part of either GC route - trains via High W diverged from the GW/Chiltern route further out at Ashendon Jn and ran to Grendon Underwood Jn

Fair - and that would likely have survived if the GC did. Would have been interesting to see whether or not Grendon Underwood Jn would have been rebuilt to give 100+ to the route to Ashendon Jn if it had remained as main route to London. Although I agree with an upthread suggestion that High Wycombe-London would probably need 4-tracking.

 

[Nottingham59]

what speeds could have been acheived assuming the route remained within its original boundary.

Looking at https://www.railmaponline.com/UKIEMap.php , I'd say that the tightest curves north of Aylesbury were about 1000m radius, though there is one between Leicester and Lutterworth that I reckon is 800m.

HS2 specified 4000m curves for a 400km/h, so 1000m should be good for 200km/h = 125mph. (Radius varying with the square of teh speed)

 

[mike57]

Looking at https://www.railmaponline.com/UKIEMap.php , I'd say that the tightest curves north of Aylesbury were about 1000m radius, though there is one between Leicester and Lutterworth that I reckon is 800m.

HS2 specified 4000m curves for a 400km/h, so 1000m should be good for 200km/h = 125mph. (Radius varying with the square of teh speed)

Not seen that website before, thanks for posting the link, makes interesting viewing.

 

[quantinghome]

Looking at https://www.railmaponline.com/UKIEMap.php , I'd say that the tightest curves north of Aylesbury were about 1000m radius, though there is one between Leicester and Lutterworth that I reckon is 800m.

HS2 specified 4000m curves for a 400km/h, so 1000m should be good for 200km/h = 125mph. (Radius varying with the square of teh speed)

That's not right.

The formula relating curve radius to linespeed is:

E+D = 11.82 * v^2 / R

E+D = Cant + Cant Deficiency

v = speed (kph)

R = curve radius

Maximum E+D in the UK for modern track is 150mm + 110mm = 260mm

This gives the following radii for given linespeed:

Speed - Radius (rounded to 100m)
160kph - 1200m
200kph - 1800m
250kph - 2800m
300kph - 4100m
360kph - 5900m
400kph - 7300m

These are minimum radius values based on maximum cant and cant deficiency. You'd want to relax them if possible to reduce track wear. For a 125mph railway, you should be looking at around 2500m radius curves.

The GC extension was designed as a 80-90mph railway. It's not particularly straight - certainly not as straight as the GWR. It would have been possible to up the linespeed to 125mph but it would have needed some significant track realignment to do so.

 

[mr_jrt]

From what I recall, in the alternatives to HS2 documentation that was produced, "Rail Package 2" was a list of upgrades that could be applied. Obviously these worked out worse value for money than HS2, but the reason I mention them is because they went into detail about upgrading the Chiltern line to provide more capacity. Aside from all the obvious interventions, they proposed a long bypass of High Wycombe, which would have made 125mph possible all the way, which given how straight the NNML was, I suspect means all the way from Paddington/Royal Oak/OOC.

 

[quantinghome]

From what I recall, in the alternatives to HS2 documentation that was produced, "Rail Package 2" was a list of upgrades that could be applied. Obviously these worked out worse value for money than HS2, but the reason I mention them is because they went into detail about upgrading the Chiltern line to provide more capacity. Aside from all the obvious interventions, they proposed a long bypass of High Wycombe, which would have made 125mph possible all the way, which given how straight the NNML was, I suspect means all the way from Paddington/Royal Oak/OOC.

Yeah, IIRC it was basically 4-tracking the Chiltern line and upgrading to 125mph to allow all the Birmingham services to be transferred.

 

[Nottingham59]

That's not right.

The formula relating curve radius to linespeed is:

E+D = 11.82 * v^2 / R

E+D = Cant + Cant Deficiency

v = speed (kph)

R = curve radius

Maximum E+D in the UK for modern track is 150mm + 110mm = 260mm

This gives the following radii for given linespeed:

Speed - Radius (rounded to 100m)
160kph - 1200m
200kph - 1800m
250kph - 2800m
300kph - 4100m
360kph - 5900m
400kph - 7300m

These are minimum radius values based on maximum cant and cant deficiency. You'd want to relax them if possible to reduce track wear. For a 125mph railway, you should be looking at around 2500m radius curves.

The GC extension was designed as a 80-90mph railway. It's not particularly straight - certainly not as straight as the GWR. It would have been possible to up the linespeed to 125mph but it would have needed some significant track realignment to do so.

Yes, you're right. I was quoting from memory. In fact, HS2 uses curves of 8,200m radius for an alignment compatible with 400kph running without tilt, according to the HS2 Route Engineering Study https://www.railwaysarchive.co.uk/documents/HS2_RouteEngineeringStudyChapter1to4_2010.pdf

Which means that 1000m curves would correspond to 140kph = 87mph. In broad agreement with your figures.

But you can go faster than that with tilt. The tightest curves on the WCML seem to be about 1200m, (though there is one at 1000m in Rugby and 6-700m radius at Stafford). So the GC would have permitted Pendolino speeds just a bit slower than the WCML.

 

[zwk500]

But you can go faster than that with tilt. The tightest curves on the WCML seem to be about 1200m, (though there is one at 1000m in Rugby and 6-700m radius at Stafford). So the GC would have permitted Pendolino speeds just a bit slower than the WCML.

It's worth remembering that the WCML isn't 125mph throughout, even on EPS.

 

[Bald Rick]

It's worth remembering that the WCML isn't 125mph throughout, even on EPS.

certainly not round the curve at Stafford!

 

[Irascible]

Fair - and that would likely have survived if the GC did. Would have been interesting to see whether or not Grendon Underwood Jn would have been rebuilt to give 100+ to the route to Ashendon Jn if it had remained as main route to London. Although I agree with an upthread suggestion that High Wycombe-London would probably need 4-tracking.

As a small aside, the top half of it *did* survive until not that long ago - given the GC ends at Calvert there wasn't much point keeping the south end though.

--

So, once you've rebuilt all the stations to straighten things out, and then counted the added expense of tilt, what do we have? how many stations are sited well enough to be worth stopping at? how much time have we saved to spending money on the MML too

 

[zwk500]

certainly not round the curve at Stafford!

Indeed.

FWIW - the 401.5 miles from Euston to Glasgow is scheduled to take 4h31, with 6 stops. 12.5mins is dwell, plus another 12mins or so braking/acceleration for the stops so let's say 25min total saved if running non-stop. 401.5 miles in 4h06 is an average speed of 98mph.

 

[Bald Rick]

Indeed.

FWIW - the 401.5 miles from Euston to Glasgow is scheduled to take 4h31, with 6 stops. 12.5mins is dwell, plus another 12mins or so braking/acceleration for the stops so let's say 25min total saved if running non-stop. 401.5 miles in 4h06 is an average speed of 98mph.

I make it 4h30 (1S52) with 6 stops, 12.5 dwell, 14.5 allowances, and I’d allow an average of 1min for each braking / acceleration, but not for Euston or Glasgow, so 10 mins. That’s 37 min off, meaning a base time of 3h53, average of 103.4mph.

Not coincidentally, the northbound Pendolino record attempt was 3h53…