The A48 Neath by-pass road between Baglan (NGR: SS 7405 9390) and Lon-las (NGR: SS 7082 9721) is some 5.3km long. It includes at its southern end two steel viaducts (nprn 91603 & 91604) to cross the River Neath Navigation (nprn 91663), Neath Canal (nprn 34444), Briton Ferry Dock (nprn 34237), the South Wales Railway main line and various minor railways and roads. Construction of this 'bridges' section was started in 1949 and it opened in 1955 between Baglan roundabout and Earlswood roundabout (NGR: SS 7299 9432) where it joined the A483 Fabian Way (nprn 410100) providing a link to Swansea Docks; the section between Earlswood and Lon-las was opened in 1960. The road is still in use although superceded by, and partially converted into, the M4 motorway. A 470m length of the original dual carriageway alignment remains near Lon-las at NGR: SS 7120 9700.
(Meccano Magazine, March 1956, p.125)
B.A.Malaws, RCAHMW, 11 January 2010.