Thanks all; very useful.

There a some lines around Bristol (and Wiltshire!) which could benefit from re-doubling, and I have always assumed that if an alignment once had two tracks it should be piossible to re-double it without needing to acquire land.

I can see now that this may not always be the case -although thanks to Brunel, we may have more wiggle room than some!

 

I've been having a ponder over any problem points for redoubling on The Beach Line, a line that I'm reasonably familiar with and which is relatively short but which may need additional passing loops for a more "metro like" frequency. 
Pleasingly, I'm hard pushed to think of any, save perhaps the railway arch over the A38 Gloucester Road (or is it Cheltenham Road there?).  Could there be gauge or weight restriction issues there?

 

It is Cheltenham Road there - hence the term 'Cheltenham Road arches'.

The A38 northbound doesn't become Gloucester Road until the junction with Zetland Road.

CfN (used to live in Kingsdown) 

 
With apologies for continuing the thread drift (does this warrant its own topic? Not sure...) Cheltenham Road Viaduct does look to be reasonably capacious (see Google Maps image). Clause 18 of The Great Western and Midland Railways (Clifton and Bristol) Act of 1871 implies that part or all of the line was originally built to broad guage, so I suspect they at least allowed for this - even though the iron spans of the bridge were cast in Derby, which suggests the contract may have been let by the Midland.

 

It probably does: I'll look into that this afternoon. CfN.

 

Apologies too for thread drift. AFAIK Cheltenham Road Viaduct is double-track as-built (standard not broad gauge). Assuming it's structurally sound, the problem is that if you redouble, you have to rebuild Montpelier and Redland stations which will mean lifts etc. and I suspect £10m+ each by the time you are done (not to mention they are tight sites very close to housing). IIRC, there is a plan being progressed by WECA and NR to redouble up to (St Andrews?) tunnel east of Montpelier Station with a revised junction onto the mainline which would give a significant capacity uplift for less money and minimal disruption.

 
As well as the previous noted items, the bridge over the port entrance at Sea Mills needs replacing badly.

 

I understand that according to Colin Maggs' 1975 book 'The Bristol Port Railway and Pier', the line was indeed built to standard guage, rather than broad. Of course that doesn't necessarily mean that the structures weren't built to accommodate broad guage track... and the viaduct does look to be generously-porportioned. But it seems likely that it would need to be refurbished if the line were to be redoubled.

This isn't really the point though; the question is whether the line could be redoubled without the need to acquire land. The answer to that is probably, for the most part, 'yes' - with the exception being around stations which would, as you say, need to be rebuilt to be accessible with two platforms.

The WECA plan to make Narroways Jct a double lead junction would allow a 3 tph service on the Severn Beach line. Questions have been asked about how resilient a service this would allow, however. But for a true metro-style service, 4 tph is required - and it's hard to see that being achieved without doubling all the way from Narroways to Clifton Down.

This would require reinstating second platforms at Redland and Montpelier. At Redland this may be achievable without costly lifts; Montpelier on its hillside site could be a harder nut to crack.


Yes, the state of Sea Mills Viaduct appears, to the layman's eye, shocking - rusty bits of it are falling into the mud!