Strand Underpass
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It is built within the former Kingsway tramway subway which was 20 ft wide but, because trams run on rails and thus need very little additional side clearance, it was possible to open the underpass to a single lane of northbound light traffic only in a road 17 ft wide with a clearance of only 12.5 ft. This latter restriction was due to the access from the bridge - a 1 in 12 gradient - having to avoid the abutment holding the bridge in place. An electronic 'eye' alerts drivers of tall vehicles and diverts them to an 'escape route' to the left of the entrance however high vehicles do still try to go through and so get stuck occasionally.
Underground, the new underpass is constructed in a concrete box within the former tram tunnel: the road surface however is at the original track level. At the southern end of Kingsway the road rises to the surface on a new floor supported by metal pillars. This passes through the site of the former Aldwych tramway station but because of the greater width requirement 27 trees and some pavement had to be removed for it to be constructed.