A48(M) motorway

A48(M)
A48(M) highlighted in blue
North-Eastbound heading towards M4 junction 29
Route information
Maintained by South Wales Trunk Road Agent
Length	2.0 mi (3.2 km)
Existed	1977–present
Major junctions
Northeast end	Castleton, Newport
Major intersections	J29 → M4 motorway
Southwest end	St Mellons, Cardiff
Location
Country	United Kingdom
Counties	Newport, Cardiff
Primary destinations	Cardiff
Road network
Roads in the United Kingdom Motorways A and B road zones
← A38(M) → A57(M)

The A48(M) is a motorway in Wales that links Cardiff with Newport. It is a 2-mile-long (3 km) spur of the M4 motorway. At St Mellons, it runs continuously into the dual-carriageway A48, which also has (albeit narrow) hard shoulders. The A48(M) has no other junctions and opened in 1977.[1] The M4 was extended west from junction 29 in 1980.[2]

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The 6-mile (9.7 km) Port Talbot bypass which opened in 1966,[1] was numbered A48(M) before its incorporation into the westward extension of the M4 in the 1970s.[citation needed] Some maps show the Morriston bypass section of the M4 as also having been originally numbered A48(M), although whether this number was ever used on the ground has been questioned.[citation needed]