14 - Tanfield Arch?
(Sorry - amend to say to complete the required answer - before I read the answers above I think I knew were 1, 6, 7, 10, 12, 13 & 14. I think the Tanfield Arch is the most obscure simply because it receives remarkably little publicity for an important structure)
Actually NOT Tanfield Arch; an important structure, but the clue asks for
continuous use and in the case of the arch, "The line was later diverted, and no longer uses the bridge". The answer that I'm looking for is (!) even more obscure.
Open to all now to bridge the gaps - as many as you can -
1 - Glenfinnan - BobM
2 - Barmouth - TonyN
3 - Calstock - bradshaw
4 - Meldon Viaduct - DR7835
5 - Bennerley Viaduct - Merthyr Imp
6 - Maidenhead - Witham Bobby
7
8 - Reedham Swing Bridge - JayMac
9
10
11
12
13 - Conway Bridge - Oxonhutch
14
15 - Sloane Square - PrestburyRoad