The A48 is a trunk road in Great Britain running from the A40 at Highnam, 3 miles (4.8 km) west of Gloucester, England, to the A40 at Carmarthen, Wales. Before the Severn Bridge opened on 8 September 1966, it was a major route between England and South Wales. For most of its route, it runs almost parallel to the M4 motorway. During times of high winds at the Severn Bridge, the A48 is used as part of the diversion route and is still marked as a Holiday Route.

The A40 is a trunk road which runs between London and Goodwick (Fishguard), Wales, and officially called The London to Fishguard Trunk Road (A40) in all legal documents and Acts. Much of its length within England has been superseded by motorways, such as the M40, and has lost its trunk road status, though it retains it west of Gloucester, including its length within Wales. It is approximately 260 miles (420 km) long. The eastern section from Denham, Buckinghamshire to Wheatley, Oxfordshire is better served by the M40 and its former function of linking London with Cheltenham and Gloucester has been taken by the M4, A419 and A417 via Swindon.