GC loading gauge

[Bald Rick]

I was intrigued by this question, so for my exercise today I cycled to Whitwell Farm Cutting nature reserve, just south of Nottingham . The bridge there crosses a double track section of what was the GC main line.
View attachment 76227
From the colour of the bricks and the design, I think the bridge there is an original dating from 1899. The structure gives 7.93m clearance between the vertical sides and is 5.37m tall from the ground to the centre of the arch, measured by a handheld laser tape measure. I don't know how these dimensions compare with other lines - I'll see if I can measure a bridge on the MML from above somehow.

Anyway, I overlaid this image with the MS&LR clearance diagram that HWL so kindly pointed us to, scaling it against the far edge of the arch (i.e. against the inner black arc in the image)
View attachment 76228
There seems to be plenty of room horizontally, but not that much vertically. So my guess is that this bridge was designed to allow the possibility of having wider rolling stock at a later date.

Or that over time the ground level has built up naturally to be higher than rail level.

 

[edwin_m]

I suspect by the time of the GC London Extension they had enough knowledge to know what the curve radii were for the chosen line speed and didn't waste money designing larger curves. Sometime I'll try and work through the Ordnance Survey maps and try to prove or disprove that by looking for places where a long gentle curve would have done just as well as two straights with a tighter curve in between. The design speed would have been around 100mph, as they probably didn't anticipate a train going faster than that, so trying to do so would involve a lot of re-alignment.

The Stephensons and contemporaries probably under-estimated the speed that trains would run as well, and by a greater amount in an earlier era. Not sure whether the physics of cant and cant deficiency or the tolerances of people and equipment to same were known to Brunel's, but he had a reputation for designing far in excess of sensible requirements anyway.

 

[edwin_m]

Or that over time the ground level has built up naturally to be higher than rail level.

I think on the left of the picture the abutment built out by one course of bricks. Isn't that something that's normally done for a few courses above ground level? The link below shows the same feature on a similar type of GC bridge as built, thought to be not far from the one pictured above. To me the rail level looks about right considering it's referenced to the far side of the structure.
https://www.railwayarchive.org.uk/getobject?rnum=L1179

I actually think there's not much room horizontally as shown, considering that the profile is a load gauge and therefore static. The kinematic gauge has to allow for quite a bit of sway at cantrail level. However I also think the track spacing is a bit more than six feet on that montage. Making it a little narrower might allow for slightly wider trains while still preserving the normal separation when they pass.

 

[PartyOperator]

Do you have a link to more information about this aspect of the GWML?

I suspect the idea of Brunel designing for 200mph is another one of those urban legends around broad gauge etc. (which technically would be better for very high speeds but isn't necessary), though it might be true given his ridiculous over-engineering. Anyway, I found a presentation (link below) which indicates that about 75% of the GWML route mileage has >5000m curve radius and there's a much smaller proportion at <2800m (which is OK for ~150mph) than the MML. I think 200mph needs >4000m. It's largely irrelevant (other than being good for rail wear), but the majority of the line between Acton and Wooton Bassett at least is remarkably free of tight bends.

https://www.thepwi.org/about_us/blo...different_elements_are_important_latest_mixes

Regarding Brunel's plans, I found some evidence given to a committee in the planning phase - the questioner posits that one mile was an appropriate minimum, and Brunel replies that it's not enough and he would prefer much more... It seems that 1 mile radius did become an accepted standard and was fine for 100mph trains, Brunel was just overdoing things as usual. But he did get away with it and the railway ended up with much larger curves than most others.

https://books.google.co.uk/books?id=2-MNAQAAMAAJ&pg=RA1-PA24&lpg=RA1-PA24#v=onepage&q&f=false

Q: To what extent have you any curve upon the line that might operate upon the locomotive engines?
A: The curves are very slight.
Q: What is the radius of the smallest curve?
A: Slight. In London there is one of 3 miles diameter [i.e. 1.5 miles radius] a small portion of it; after that they are all 4, 5 or 6 miles.
Q: Has it not been ascertained by experiment that any thing below a mile radius diminishes the friction so as not to impede the engine?
A: A mile radius is not desirable.

 

[Nottingham59]

I'd be interested to hear if any original GC structures were built with less than the 7.93m clearance between the sides. There's a Great Central Walkway near Rubgy that would be a good place to check:
https://www.google.co.uk/maps/@52.3...XGX58s7hzMwj2kfzp1-Mt!2e10!3e12!7i5376!8i2688

 

[Gostav]

I suspect by the time of the GC London Extension they had enough knowledge to know what the curve radii were for the chosen line speed and didn't waste money designing larger curves. Sometime I'll try and work through the Ordnance Survey maps and try to prove or disprove that by looking for places where a long gentle curve would have done just as well as two straights with a tighter curve in between. The design speed would have been around 100mph, as they probably didn't anticipate a train going faster than that, so trying to do so would involve a lot of re-alignment.

The Stephensons and contemporaries probably under-estimated the speed that trains would run as well, and by a greater amount in an earlier era. Not sure whether the physics of cant and cant deficiency or the tolerances of people and equipment to same were known to Brunel's, but he had a reputation for designing far in excess of sensible requirements anyway.

But how fast they can do when train bypassing the island platform? I visited GCR(L) Railway and believe the curvatures for bypass island platform stations are not ideal for high speed.

 

[Peter Kelford]

But how fast they can do when train bypassing the island platform? I visited GCR(L) Railway and believe the curvatures for bypass island platform stations are not ideal for high speed.

They're goods loops I think.

 

[edwin_m]

But how fast they can do when train bypassing the island platform? I visited GCR(L) Railway and believe the curvatures for bypass island platform stations are not ideal for high speed.

This is probably one reason island platforms aren't so common despite ostensibly needing less land and facilities. The distance over which the tracks have to taper either end is surprisingly large, increasing land take and also the size of any bridges at either end of the station (I believe every GC London extension station has at least one). I would guess the GC designed the reverse curve for no more than their expected speed of 100mph (if anyone wants to check this there are plans at www.railwayarchive.org, no radii shown but it might be possible to work out from the length of the taper).

If this is so then increasing the speed would require either demolishing the platform and probably modifying said bridge, or lengthening the taper which may involve buying more land.

Some stations had goods loops outside the main running lines as well. The speed through these wouldn't be critical as anything using them would stop anyway, but the pointwork for them would probably be in the area of the taper so if the loops were kept that would most likely need modifying too. Alternatively if the loops were abandoned it's possible the main lines could be re-aligned for higher speeds within their footprint.

 

[Flying Phil]

Certainly by the time the line closed, the platform to stock spacing was not generous as, I believe, when the Continental "King Haakon" first ran, they had to shave the edges off the platform stones to get the cylinders through!

 

[edwin_m]

Many years ago I had the job of organizing some tests of a foreign coach which had come to the UK to be converted to a track recording vehicle. The GC could only accommodate it if we paid to have the platform copings removed and later put back, but the Nene Valley could take it without any work, subject to speed restrictions on a couple of bridges. Unfortunately our PR department ruled out steam haulage.

 

[Peter Kelford]

Many years ago I had the job of organizing some tests of a foreign coach which had come to the UK to be converted to a track recording vehicle. The GC could only accommodate it if we paid to have the platform copings removed and later put back, but the Nene Valley could take it without any work, subject to speed restrictions on a couple of bridges. Unfortunately our PR department ruled out steam haulage.

Looking at photos of the GC heritage stations, it is quite clear that there has been some additional protrusion from the platform edges which doesn't appear to date from the same era as the rest of the platform...I wonder if that is something to do with the GC heritage line rather than GCML.

 

[Merle Haggard]

Many years ago I had the job of organizing some tests of a foreign coach which had come to the UK to be converted to a track recording vehicle. The GC could only accommodate it if we paid to have the platform copings removed and later put back, but the Nene Valley could take it without any work, subject to speed restrictions on a couple of bridges. Unfortunately our PR department ruled out steam haulage.

I think that the handicap on the LNWR loading gauge was platform coping and it seems all the Nene Valley had to do to accept stock from mainland Europe was to set the platform coping back.
The LNWR situation may have arisen from their widespread use of low platforms - in my trainspotting youth even stations on the WCML had low platforms; for instance, the surface of those at Roade was about level with the mid-point of the axlebox covers on a coach. When the extra springs were fitted to produce 86/2s these were very close indeed to the coping at Northampton which of course had 'normal' height platforms..

 

[talltim]

Also I seem to recall that the main line North from Marylebone was built with absolutely no level crossings ?.

Well, the London extension was built south from Sheffield (Woodhouse), but..
There is one level crossing on the route, at Beighton, now on the link from the GC to the Midland 'Old Road.
https://www.google.co.uk/maps/@53.3508662,-1.335137,223m/data=!3m1!1e3

 

[edwin_m]

Well, the London extension was built south from Sheffield (Woodhouse), but..
There is one level crossing on the route, at Beighton, now on the link from the GC to the Midland 'Old Road.
https://www.google.co.uk/maps/@53.3508662,-1.335137,223m/data=!3m1!1e3

Didn't it officially start from Annesley, the route southwards presumably having been built that far before the GC decided to head for London? Certainly that's where the plans start (with Sheet No 1) on the site I linked above.

 

[Rob F]

Didn't it officially start from Annesley, the route southwards presumably having been built that far before the GC decided to head for London? Certainly that's where the plans start (with Sheet No 1) on the site I linked above.

Correct, the London Extension started from Annesley.

 

[Nottingham59]

The bridge ... crosses a double track section of what was the GC main line.... The structure gives 7.93m clearance between the vertical sides

For exercise last night I went out and measured the width of the Lady Bay bridge in Nottingham. This was built by the Midland Railway in the 1870's (I believe) to carry express trains to London from Nottingham bypassing the gradients on the route via Leicester. This was quite late in the railway building era, but before the GC.
https://www.google.co.uk/maps/@52.9...4!1s_9u5PuJU2g-s01yFBKQxMQ!2e0!7i13312!8i6656

The distance between the flat faces of the stone pillars (see link) varied by a few centimetres along the bridge, but the narrowest gap was 7.92m, exactly matching the GC bridge at Whitwell Farm. Is this just a coincidence? Or had this generous structure gauge become the norm for British mainlines by that stage, I wonder? But anyway, we can say that the GC was not built uniquely wide.

I'd be interested to see how these figures compare with earlier structures elsewhere on the Midland network or the MS&LR.

 

[Nottingham59]

And today I went to measure bridge 301 near Gotham. The line here is level with the surrounding fields, and the crossing track is on a ramped embankment so there would be no reason to build the bridge any higher or wider than the structure specifications for the line.



The bridge opening is 7.87m wide and is 4.26m high, measured from the top of the rail. So I reckon this bridge, at least, was built to allow for the future use of rolling stock that was much bigger than the British standards at the time, and comparable with European rolling stock at the end of the nineteenth century.

The Gabarit PPI gauge, defined 13 years later in 1912, is 3.150m wide by 4.280m tall. So there's not quite enough height to take that (unless the ballast bed has got deeper over time). But there is enough width, I think, as shown in this montage of German G1 gauge (also 3150x4280mm) scaled as best I can against the structure.


So I reckon lowering the track bed by 3cm would allow Berne stock to fit. What do other people think?

 

[norbitonflyer]

The confusion probably arises from a misunderstanding. The UIC has a number of loading gauges known as GA, GB, GB+, GC in increasing size - the "G" standing for "gauge" ("gabarit" in French). As it happens, most German railways conform to GC and most French ones to GA, although TGV lines are built to GB. It is easy to see how GB and GC could be misunderstood to be, respectively, the dimensions used in the UK generally, and the Great Central Railway.

 

[Peter Kelford]

The confusion probably arises from a misunderstanding. The UIC has a number of loading gauges known as GA, GB, GB+, GC in increasing size - the "G" standing for "gauge" ("gabarit" in French). As it happens, most German railways conform to GC and most French ones to GA, although TGV lines are built to GB. It is easy to see how GB and GC could be misunderstood to be, respectively, the dimensions used in the UK generally, and the Great Central Railway.

GC is now recommended on high-speed lines. GB is also not to be confused with G1/PP1/Berne Gauge. French LGVs are built to GC standards. FR 3.3, a tad larger than GA is used on a large part of the classic network.

 

[InOban]

Am I right that the main problem with converting to any of these European gauges is that they carry their width down much lower to suit their lower platforms?
Over much of our network the cost of changing every platform is what prevents the conversion of W10/12 to a continental gauge, more than issues with bridges.

 

[Nottingham59]

Yes, fitting the trains between the platforms has always been the problem with adopting wider loading gauges in Britain. But the whole point about the design of the Great Central was that the stations were built with a single central platform and generous bridges, to allow for future upgrages. Firstly you could convert to wider rolling stock simply by re-laying the track further away from the platform facings; and secondly there was space to build fast lines outside the stopping lines to allow overtaking. But it is a point for discussuion just which of these options (or both) were originally intended.

 

[grumpyoldman01]

Attached is a copy of Francis Douglas Fox's presentation to the Institution of Civil Engineers regarding the construction of the southern section of the GC Main Line.

It includes a cross section of the loading gauge, and lists - page 25 - minimum dimensions for bridges (height and width); minimum radius of curves was one mile (with one exception, but it doesn't say where). Fox also states (on page 28)
"In order to economize in land, to enable the stations to be worked with the smallest possible staff, and to make future widening to four lines of way as easy and cheap as possible, the “ island ” platform system was adopted". He also states that the line was designed for high speed, but of course what was seen as high speed then isn't necessarily classed as high speed now.

However, in one of the reports Atkins produced for the DfT in connection with HS2 alternatives, there's a graph showing theoretical maximum speeds, based upon alignment, of the GW&GC Joint Line; apart from the "bendy bit" through High Wycombe/Princes Risborough where it took the alignment of the former GWR Aylesbury branch, they concluded that it was suitable for quite high speeds (125mph+), and there's a map showing how that particular section could be bypassed (mainly in tunnel). This was only slightly after completion of the GC Main Line (final section finished in 1910), maybe he did mean 125mph+ !

I understand (from a recent article in 'Rail') that a radius of one mile isn't permitted for 125mph/200kph running in the UK, but I saw a graph some time ago - I think it was in Adtranz Sweden publicity material for the X2000 train - which showed 1500m as being suitable for 200kph for non-tilting trains, and 250kph for tilting ones. I believe the curving rules used in France permit SNCF trains to go faster through curves than British ones normally do, so if the GC Main Line was still open, could special curving rules be established to permit speeds of 125mph on curves with a radius of one mile?

 

[Peter Kelford]

minimum radius of curves was one mile (with one exception, but it doesn't say where)

I would hazard a guess at Marylebone. There were sharp-ish curves at Cosby and Great Missenden as well.

 

[grumpyoldman01]

I would hazard a guess at Marylebone. There were sharp-ish curves at Cosby and Great Missenden as well.

Don't forget Great Missenden is on the Met, so that would be discounted from Fox's claim, but I see what you mean about Cosby when looking on Googlemaps.

I only travelled on the GC Main Line between Nottingham and Victoria once (in the front seat of a class 115 DMU), but the only curve which sticks out in my memory as being "sharp" is the one round the back of Finchley Road station