I have for some time believed that a general rule of thumb was that the majority of the network was now passed for RA 8, with some noteable exceptions such as the Heart of Wales and Central Wales lines, some of the more rural branch lines, such as Liskard to Looe, and the Far North line. However, following a platform end discussion a couple of weekends ago I was informed that a lot of the Southern Region commuter lines were more of a patchwork of RA 8 and 6, depending on the traffic flows.
This got me wondering. Are there still any routes that are RA 4, and apart from those lines mentioned, are there any other notable lines that are still RA 6? By notable, I mean routes that provide a link between other routes or have a fairly regular service each day?
A good resource is to look in the Sectional Appendices on the Network Rail website - the PDF versions listed near the bottom of this page can be freely downloaded without needing a login:
https://www.networkrail.co.uk/indus...ators/national-electronic-sectional-appendix/
N.B. The file sizes (shown next to each one) are quite large!
Under the heading of "Route Clearance" there is a table for route clearance of locomotives (search for D4A and allow time for it to find the results), giving the official RA for each route. Where a loco type exceeds the route RA, these tables determine whether the loco type is allowed on the route or not, and sometimes lists speed restrictions (usually over specific bridges). Clearance for locos with an RA in excess of the route RA is given here (or not), while wagons require RT3973HAW (heavy axle weight) paperwork if they exceed the route RA, as discussed above.
On the former Southern region, low RA routes (below 8) are mainly concentrated in South London - possibly due to lines running on arches - and on some passenger branch lines that are not through routes (possibly ones where the structures on the route were originally designed for tank engines rather than the heaviest steam locos?). In terms of through routes, I think the most notable low RA routes are Gillingham (Dorset) towards Exeter - already mentioned as being RA6, Fareham to St Denys (RA7), Ashford to Hastings (RA7) and Castle Cary to Dorchester (RA6). The exact boundaries for the different RAs can be seen in the sectional appendix. Of these, I think Gillingham (Dorset) to Pinhoe and Ore to Ashford are prohibited to any freight traffic heavier than RA8 (i.e. there is an RT3973HAW form but it only covers RA7 and RA8 wagons in excess of the normal RA6 restriction for the route).
One oddity on the former Southern Region is that there is a blanket 50mph restriction for RA10 freight traffic (where authorised). I can't remember the reasoning behind this - possibly signal spacing and stopping distances?
What I am getting is that in principle the RA value for a specific route is used for "general" services, whereas there are documented processes that permit heavier train loads but with very specific restrictions across some, but not all, low value RA routes.
What items would restrict the RA on any given route? Is there anything else other than:
* weight restrictions on over bridges, viaducts, culverts etc;
* the permanent way, such as the type and strength of rail used, together with how the ballast is built to distribute the weight on to the underlying ground;
* underground workings, such as mine shafts, caves, water routes and similar man made items;
The Western Region sectional appendix is interesting as it has "Table D5A - Route clearance of freight vehicles" which sets out the maximum RA that can be accommodated in excess of the route RA on each section of line. This lists the speed restrictions that form the basis of the "RT3973HAW" paperwork already mentioned. One oddity is that the Whatley quarry branch is RA6 despite being used for heavy quarry traffic - presumably for historical reasons as there don't seem to be any extra speed restrictions for RA10 traffic.
I think the vast majority of restrictions that lower route RA are related to structures - underbridges, culverts, viaducts, arches. A while ago I read an article on how RA is calculated - it was a bit technical but my general understanding was that the most important consideration was the force transferred to a structure (e.g. a viaduct or bridge) in the direction of travel. So the weight of a train pressing down on a bridge is one thing, but there is also a component of that weight which is effectively pushing against the bridge supports in the direction of travel. It makes sense that reducing speed would reduce this force (hence the speed restrictions on RT3973HAW forms), even though it does nothing to alter the weight of the train. Axle spacing in addition to axle weight also made a difference to the calculations, with some of the shorter types of bogie coil carriers (for example) having a higher RA than pure axle weight would suggest. I think suspension characteristics of certain types of wagons also made a difference in some cases.
I'm not sure that the rails and ballast used have much bearing on these issues - I think most routes these days would use standard types of rail such as 56E1 (56kg per metre) and also be ballasted in a fairly standard way. I'm also not sure if ground conditions are a common reason for lower route availability. I think they do impact speeds as a whole (I remember a discussion on this forum about the line out to Cleethorpes saying the ground conditions made it difficult to improve line speeds) but I've not heard that as an influence on RA issues. One exception might be where a route was specifically built originally as a "light railway." The Western sectional appendix quotes the Central Wales Line (RA5) as "subject to Light Railway Order" although RT3973HAW paperwork permits infrastructure trains up to RA7. It would be interesting to get some input from someone with more knowledge from the infrastructure / engineering side of things to find out which parameters influence the authorised RA of different lines - in some cases the reasons are obvious, in others it seems a bit arbitrary.
Thinking of two lines in the north west, Trafford Park to Hunts Cross, and Phillips Park to Ashburys are both RA7. The first of these has some embankments that could potentially have issues, but I suspect the main reason the route is RA7 is due to structures like
Warrington viaduct (photo: 8A Rail) or the
viaduct over the Manchester Ship Canal at Irlam (photo: Peter Ashton). I recently watched a cab ride video on the route from Phillips Park to Ashburys, and there are a couple of long bridges plus a section near Ashburys where the route is running on arches (labelled as Beswick arches on google maps with a photo). Class 67s are prohibited over both routes, but both routes allow RA10 freight traffic with an RT3973 form (although the route through Warrington Central prohibits HTAs in excess of 96 tons gross weight).
How about engineering/possession trains on RA5 branches? Locos would be RA7 or 8? How does that work?
As per post #10 the wagons are covered by RT3973HAW paperwork (for example wagons up to RA8 are permitted on the East Grinstead (RA6) and Uckfield (RA4) branches. However, if you look in the sectional appendix, class 66s are prohibited from these routes! The usual practice is for the structures engineer to issue temporary paperwork authorising the use of class 66 locomotives for planned engineering work (subject to speed restrictions in certain places). On other branches with a lower RA than a 66, the authorisation is listed in the route clearance tables in the sectional appendix.
