Combe Down Tunnel
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Combe Down Tunnel is a tunnel on the closed Somerset and Dorset Joint Railway main line, between Midford and Bath Queen Square, below high ground and the southern suburbs of Bath, England at Combe Down.
The whole tunnel is on a gradient of 1 in 100[1], climbing towards Bath, and at a mile long is the longest railway tunnel in the UK without a ventilation shaft.
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[edit] Overview
The tunnel was on the Bath extension line of the Somerset & Dorset Railway, built in 1874. The extension effectively bankrupted the independent company. The extension line was later made double-track northwards from Evercreech Junction to the viaduct at Midford, but the substantial civil engineering works associated with the tunnel and the steep approach into Bath, including the shorter Devonshire tunnel, caused the northernmost section to remain single-track throughout its working life. Trains heading south from Bath were often banked (assisted in rear) by a locomotive that detached itself from the train at the entrance to Combe Down tunnel, and then returned back down the gradient to Bath.
[edit] Accident
Combe Down tunnel had no intermediate ventilation and there were significant problems with fumes. On one occasion in 20 November 1929, the driver and fireman of a northbound goods train were overcome by smoke. The train was moving very slowly in the tunnel due to a heavy load and due to starting from a standstill at Midford. The 7F 2-8-0 locomotive plodded on and eventually breasted the summit of the gradient. Its downward course to Bath was accomplished more quickly, and the train ran away, crashing into the goods yard on the approach to Bath Queen Square railway station, killing the driver and two railway employees in the yard.
The fumes that overcame the footplate crew were a consequence of the restricted bore, lack of ventilation shafts, the exceptional humidity and lack of breeze, and the very slow speed of the train, running tender first. The inspecting officer, Col A C Trench recommended that maximum loads should be reduced or assistant engines provided to prevent a recurrence[2].
[edit] Two Tunnels Shared Path
This section of the Somerset and Dorset Railway, including the tunnels, is proposed for a shared use path, and planning permission for this was achieved in November 2007.
[edit] References
- ^ Gradients of the British Main-Line Railways, Railway Publishing Co Ltd, London 1947
- ^ Rails to Disaster: More British Steam Train Accidents 1906 - 1957, Gerard, M and Hamilton J A B, George Allen and Unwin, London, 1984, ISBN 0-04-385103-7
