The Bristol Port Railway and Pier company (BPRP) ran from a main terminus at Hotwells (originally called Clifton), northwards to west of Bristol city centre between the Clifton Suspension Bridge and Bridge Valley Road, to a terminus at Avonmouth. Upon leaving Hotwells, the line ran north alongside the River Avon through two tunnels, to a halt and passing point, then to Sneyd Park Junction, where the Clifton Extension Railway joined it. Continuing north following the river is the station at Sea Mills, then a bridge over the River Trym. The line curved west around Horse-Shoe Bend, then went slightly inland to Shirehampton, then turned back north-west. At Avonmouth Dock Junction the Extension Railway diverged north, and another line diverged west for freight, while the BPRP line continued into the station at Avonmouth Docks. Beyond there, the line diverged again, with one line going west to Avonmouth (Royal Edward) and another north to rejoin the Extension Railway. The main BPRP line continued on into its Avonmouth terminus.
The branch was closed in 1922 to make way for construction of the A4 Portway. The two tunnels that now sit either side of Bridge Valley Road remained. Known as Tunnel #1 and Tunnel #2 they were 160m and 65m long respectively. Tunnel #1 was repurposed as an air raid shelter during world war 2. It was so popular that the council had to initiate a pass system to deal with the numbers that would attempt to use it during raids. This tunnel was then repurposed again in the 1970/80’s when Bristol Gun Club turned around 1/3rd of it into a shooting range. I explored this back in 2008
Tunnel #2 – the shorter at 65m – seems to have been converted into a ‘records store’ around 1940. There is little information on when it closed although newspaper cuttings inside would suggest it was still in use it the 1970’s. It’s entirely possible that it was in use until the end of the cold war. The other likely reason for the abandonment/closure would have been when the council moved all their archive services to the create centre only a few 100 yards further down the river.