M4 motorway

M4 motorway (eastern end)
M4 motorway
	Prince of Wales Bridge looking towards Wales
Route information
	Part of
	Maintained by ; Highways England; South Wales Trunk Road Agent
Length	189 mi (304 km)
Existed	1963–present
History	Opened: 1959 (Chiswick Flyover), 1961 (as A4(M)), 1963, 1966 (as A48(M)); Completed: 1996
Major junctions
East end	Chiswick; 51°29′23″N 0°16′41″W / 51.4897°N 0.2781°W
	; J4b → M25 motorway; /; J8/9 → A308(M) motorway/A404(M) motorway; ; J10 → A329(M) motorway; ; J19 → M32 motorway; ; J20 → M5 motorway; ; J21 → M48 motorway; ; J22 → M49 motorway; ; J23 → M48 motorway; ; J29 → A48(M) motorway
To	Pont Abraham; 51°44′42″N 4°03′54″W / 51.7451°N 4.0651°W
Location
Counties	Greater London, Berkshire, Wiltshire, Gloucestershire, Monmouthshire, Newport, Cardiff, Vale of Glamorgan, Rhondda Cynon Taf, Bridgend, Neath Port Talbot, Swansea, Carmarthenshire
Primary; destinations	; London; London Heathrow Airport; Slough; Maidenhead; Reading; Newbury; Swindon; Bristol; Newport; Cardiff; Bridgend; Port Talbot; Neath; Swansea
Road network