Rotherhithe Tunnel - Physical Characteristics

Physical Characteristics

The Rotherhithe Tunnel consists of a single bore, 4,860 feet (1,481 m) long, carrying a two-lane carriageway 48 feet (14.5 m) below the high-water level of the Thames, with a maximum depth of 75 feet (23 m) below the surface. Four shafts were sunk alongside the tunnel to aid construction and to serve later as ventilation and entrance shafts. The two riverside shafts, built in red brick with stone dressings, were fitted with iron spiral staircases to serve as pedestrian entrances. They are now closed to the public (the roofs were damaged during WWII, and the iron staircases became dangerous), and currently the only entrance to the tunnel is via the main portals at each end (the bases of the staircases can still be seen as you pass through the tunnel). Pedestrian (and cycle) access is still permitted in the Rotherhithe bore, however, the distances involved for pedestrians increased significantly when the spiral staircases closed because rather than just crossing the river, a pedestrian has to follow the carriageway ramp all the way back to the surface. However, the shafts have recently had new roofs fitted, and there are rumoured plans to reopen the spiral staircases.

The tunnel is entered via a sloping brick-lined open-air cutting at each end, leading to the entrance portals, followed by a short cut-and-cover section of tunnel until the first of the tunnel's four shafts are reached. The tunneled section is situated between shafts 1 and 4, measures 3,689 feet (1,125 m) long and is lined with cast iron segments. At the time of its construction, the tunnel was said to be "the largest subaqueous tunnel in existence".

The Rotherhithe Tunnel was originally designed to serve foot and horse-drawn traffic passing between the docks on either side of the river. This accounts for some of its more unusual design features. The roadways are narrow, with each lane only some 8 feet (2.4 m) wide, and two footways of between 4 and 6 feet (1.2 to 2 m) wide on either side. The tunnel is shallow, with a maximum gradient of 1 in 36 (2.8%), to cater for non-mechanised traffic. Its route includes sharp, nearly right-angled bends at the points where the tunnel goes under the river bed. These served two purposes: avoiding the local docks on each side of the river, and preventing horses from seeing daylight at the end of the tunnel too early which might make them bolt for the exit.

This has made it difficult for motorised vehicles to traverse the tunnel safely. Large vehicles cannot easily pass the sharp bends and are therefore banned from entering the tunnel. The speed limit is 20 miles per hour (32 km/h) and as of 2011 will be enforced using average speed cameras. A 2003 survey rated the Rotherhithe Tunnel the tenth most dangerous tunnel in the whole of Europe due to its poor safety features. Its proximity to the river also made it vulnerable to flooding, as happened in the 1928 Thames flood.