The Severn Bridge, opened in 1966, currently carries the M48 (formerly M4 [nprn 417517]) London and south Wales motorway between Aust and Beachley, replacing a ferry. There are toll booths at the eastern (Aust) end.
The bridge and its western approach over the River Wye (nprn 91661) were built 1961-6 to the design of Freeman Fox. The main bridge is a suspension type, with a welded box section deck, which was constructed in Chepstow and floated down the Wye section by section then winched into place. The Wye viaduct is of cable-stayed cantilever construction. Both sections of the bridge were substantially re-inforced in 1982-91.
The Second Severn Crossing (nprn 405), some 5km downstream, opened in 1996 to carry the M4 motorway, the road over the older bridge being designated the M48.
Sources include A Guide to the Industrial Archaeology of South East Wales, AIA, 2003
B.A.Malaws, RCAHMW, 08 June 1999 & C. Parry, RCAHMW, 4 August 2011.

Tolls had been in place on the bridge since 1966, with the original fee costing two shillings and sixpence (the equivalent of 12.5p in decimal currency). However, on 17th December 2018 the tolls were lifted on both the original and the second Severn crossing bridges, and work began to remove the toll barriers.
Source: ITV news 'Severn bridges tolls come to an end after 52 years' published online on 16th December 2017
M. Ryder, RCAHMW, 9th May 2019