Steam Era Route Availability Categories

Yes. In the accident report, the formation immediately in the area of the derailment is described thus:

"The top ballast was composed of broken Kentish rag-stone; the bottom ballast for a distance of 18 inches on each side of the centre line of the rail of half rag-stone and half beach ballast. In the centre of the sleepers and at the ends bottom ballast consisted of beach shingle mixed with binding. The depth of the bottom ballast was stated to be about 6 inches."
​

It's not clear to me what material "binding" refers to - maybe some admixture of irregularly shaped stones to stop the shingle rolling over itself. It is also curious that there was such a complex mixture in the bottom ballast, presumably by design.

The inspecting officer also wrote:

"From my examination of the down track, and from the survey made, I formed the opinion that, though the condition and strength of the rails, fastenings, and of the sleepers were adequate, the drainage, the quality of the ballast, and in particular of the bottom ballast, the gauge and the level of the rails, could not be described as first class. the road had not, I think, a sufficiently firm foundation to carry such heavy loads at high speeds as had during recent years passed over it, with the result it had gradually been knocked down. It is possible that the heavy rainfall had caused the road to go down rapidly, as stated by Mr Messer."​

There is a diagram in the accident report showing the level of super elevation throughout the curve, showing that it wandered up and down somewhat erratically, at one point being nearly 2" lower than the 3¾" it should have been on a curve of that radius. The provision of a continuous check rail on a curve of 54 chains radius also drew some comment.

Tom

 

Meanwhile my copy of “Main Line” arrived yesterday. Scanning it quickly, I notice a piece on route availability which having read this thread will earn my full attention.


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Yes, remember exploring them in the late 1960's while holidaying on Romney Marsh. There were still visible remains of Dungeness station back then, although it had been closed for at least 40 years.

 

The O4/ROD 2-8-0 is an interesting case study in regard to platform clearances. It was 8ft 10½in wide over its 21-inch cylinders, slightly narrower than a GW 28XX but still infringing the nominal loading gauge widths below platform height for most of the railways where it worked. On the LNER, it was mainly the GE and NB sections where its route availability was limited. The more you look into loading gauges, the more complicated the situation seems to become!

Interesting - I didn't know that. For another snippet, consider the Czechoslovakian locomotive classification and numbering system. The third digit indicated the axle loading, so for example a Class 475 4-8-2 had a 15-tonne axle-load.

Thanks for filling-in my hazy memory of what Holcroft had written - I'd got the colours muddled! To complete the picture, I think the King Arthurs were able to operate over the LCDR route to Dover after strengthening of the Medway crossing at Rochester in 1927, but that it was about 1934 before anything larger than a D1 or E1 could work over the coast line from Faversham to Ramsgate. By that time, the D1 & E1 must surely have been the smallest engines in Britain still used for top-link express work.

 

Valuable line that, a sort of forerunner of crossrail [grin]

 

Isn't the issue with that system that most British locos would fit in band D (15-20 tonnes)? That also encompasses three GWR weight classifications (Uncoloured, Yellow and Blue)

 

I don't think that is quite what @Dunfanaghy Road said:

- 5 axle load bands
- 5 bands of the weight per unit length, i.e. tons per metre.

The system isn't (as I understood it) axle load bands of 0-5 tons; 6-10; 11-15 etc. Otherwise you'd have 'Rocket' and not much else in band 1 while most locos were in band 4 - not very useful. In other words, five bands of axle load; not bands that are 5 tons wide.

I suspect if you chose axle load bands of below 15 tons; 15 - 17; 17-19; 20-22 and above 22; and tons per metre in various ranges up to a top range of about 7 tons per metre (i.e. a 175 ton loco 25 metres long) you wouldn't be far off.

Tom

 

OK, let's go into a bit more detail:
A = 16.0t + 5.0t/m.
B1 = 18.0t + 5.0t/m; B2 = 18.0t + 6.4t/m.
C2 = 20.0t + 6.4t/m; C3 = 20.0t + 7.2t/m; C4 = 20.0t + 8.0t/m.
D2 = 22.5t + 6.4t/m; D3 = 22.5t + 7.2t/m; D4 = 22.5t + 8.0t/m.
E4 = 25.0t + 8.0t/m; E5 = 25.0t + 8.8t/m.
On wagons if only the letter is marked it means B2, C4, D4, or E5. As all the routes are similarly classified it is fairly easy to match up the permitted weight (with, perhaps, light loading). In this country its a nightmare finding this out.
OT diversion over.
Pat

 

More on bridge stress.

https://goo.gl/maps/tbcjoButwLEm9AhJA

This is the bridge over Borough Road / Southwark Bridge Road in South London, on the LCDR Metropolitan Extension.

The original bridge is the dark green; it consists of two large wrought iron box girders (the longer of which is 170 feet long); braced at 40" centres with cross girders. The rails were carried on wooden transoms. It dates from 1864.

In 1909, it was discovered that the bridge was subject to high bending and shear stresses. The chosen method of strengthening was to add the truss girder over the top, now painted a pale colour. (The reason for that method of repair was to minimise disruption to the tram traffic below while the strengthening was carried out).

Which is largely just anecdata, but shows that by teh early twentieth century, the mainline companies were having to get to grips with a programme of bridge strengthening as train weights increased.

Tom

 

In the West Country, Mr Brunel's wooden-topped viaducts needed replacement in the late 19th/early 20th centuries. The pillars often still stand alongside the newer viaducts.

Another example is from the GCR at Dinting, which was strengthened in 1918-20 by having additional piers inserted, of a different shape and style to the originals. Clearly did the job, but nil points for aesthetics.

https://en.wikipedia.org/wiki/Dinting_viaduct

 

Its well documented that the GWR instituted a new standard of 22 tons axle load for bridge construction and reconstruction around 1904. I believe Brunel's Royal Albert bridge was strengthened in the 1900s, the 1930s, the 1960s and 2011...

On the topic of route planning, my understanding of the NR docs I took a look at is that each structure is allocated an RA number in the NR database, which should make it possible for software to calculate a route for any given load. I don't know to what extent this is fully implemented though. Its a better way to do things though rather than designating a whole line as unavailable because of one structure

 

I am now curious to know as to why painting it a pale colour minimised disruption to tram traffic...? Were tram drivers easily spooked by dark colours...

Hammerblow is clearly a huge part of this. Does anyone have the link to that phd thesis on the history of it? It was part of what dragged me onto this place...

As a final thought - is gauging considered partof RA? Given the generally closer fit between structures and envelope here than in much of Europe, does this explain why the apparently simply UCH axle-load code never caught on here?

 

RA and loading gauge are separate issues.
The difficulty with our system, and total reliance on TOPS (i.e. IT ) is that there is no easy way (that I know of) for working out how to load a wagon to a restricted RA, other than trial and error. Not a problem with engines, of course.

(I think Tom's reference to the colour of the reinforcement at Borough Road was to identify the bit in question.)

Pat

 

I know, but it's a wonderful mental image
[Harry Enfield Cheomondley-Warner sketch style] "we need to reinforce the bridge sir, but the tram drivers will object"
"Don't worry, we'll paint it a lighter colour and they'll never notice"

Re wagons etc - if RA is axle load, can you not just load them to the axle load on the booked route? Presumably when RA was first done, RCH-pattern wagons had such a light axle load at 13ton tare over 2 axles (and with no hammer-blow) would mean they were on nobody's radar when looking at RA (as the engine would both weigh more statically, and after dynamic load was considered, be even more so)

 

Once upon a time - on a railway far, far away - BR wagons had a data panel showing (for 4 conditions: Empty; Light; Medium; Heavy) the Total weight, RA, Brake force, and , also, the length. TOPS rendered this unnecessary (so the suits said). The dodge in GB-land (and the Continentals may have something similar) is the 'Advice to Train Crews' form (RT3973) given to a driver if any of his train exceeds the RA for the route. (Not the engine, it's the drivers job to know that.) RT3973HAW lays down the maximum speed at the crucial locations (Bridges in the case of RA) due to Heavy Axle Weight. RT3973EXL does the same for structure clearances (to pick up an earlier comment).
Pat