SEmG

Railway Structures
Tunnels

Esher footbridge Tunnel at Crystal Palace, photographed on 13th September 2009.

photograph by Gregory Beecroft

In engineering terms, a tunnel is normally regarded as a structure with overburden, such as soil or rock. However, there are some structures which are strictly speaking bridges, but are treated by the railway as tunnels. This is usually because they impose operating or inspection and maintenance constraints similar to those of a tunnel. Examples include buildings on rafts over the railway, for example at Woolwich, and wide bridges with restricted clearance, as at Fulwell.

When a cutting would need to exceed 60 feet in depth, it was usually more economic to construct a tunnel. Particularly difficult ground conditions or a requirement for a large volume of material for embankments, might make a deeper cutting preferable. Some tunnels were not necessary, but had to be constructed to meet the requirements of influential landowners.

Although South East England is low-lying, it is quite hilly. If any type of major structure typifies the Southern, it is tunnels, as the following comparison shows.

Route Total length of tunnels Tunnel length as % of route
Charing Cross to Dover Priory
Victoria to Brighton
Euston to Glasgow
King's Cross to Edinburgh
7 miles 619 yards
3 miles 1,623 yards
4 miles 1,034 yards
4 miles 962 yards
9.5%
7.7%
1.2%
1.2%

Southern tunnels more than a mile in length are listed below. All except Penge Tunnel are through the North or South Downs. There are few lengthy tunnels on former London & South Western Railway lines, the longest (apart from the Waterloo & City Line) being Honiton Tunnel at 1,345 yards.

Tunnel Length Location
Sevenoaks
Polhill
Lydden
Strood
Oxted
Clayton
Penge
Quarry
Abbotscliffe
Merstham
1 mile 1,693 yards
1 mile 851 yards
1 mile 609 yards
1 mile 569 yards
1 mile 501 yards
1 mile 499 yards
1 mile 381 yards
1 mile 353 yards
1 mile 182 yards
1 mile 71 yards
Sevenoaks - Hildenborough
Knockholt - Dunton Green
Shepherds Well - Kearsney
Higham - Strood
Woldingham - Oxted
Hassocks - Preston Park
Sydenham Hill - Penge East
Purley - Earlswood (via Quarry Line)
Folkestone Central - Dover Priory
Coulsdon South - Merstham

There are much longer tunnels on High Speed 1. London Tunnel 1, between St Pancras International and Stratford International is 7,543 metres long (up) and 7,529 metres long (down). This is exceeded by London Tunnel 2, between Stratford International and Dagenham, at 10,120 metres. The Thames Tunnel is 3,121 metres long and the North Downs Tunnel is 3,199 metres long.

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