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.