The South Wales Trunk Road Agent (Welsh: Asiant Cefnffyrdd De Cymru) (SWTRA) is responsible for managing motorways and trunk roads in South Wales on behalf of the Welsh Government. The South Wales Trunk Road Agency was established on 1 April 2006, and by 1 April 2012 it was renamed the South Wales Trunk Road Agent. The South Wales Trunk Road Agent is responsible for the motorway and trunk roads from the Severn Bridge in the East to Milford Haven in the West.
Prior to the South Wales Trunk Road Agency being established, motorways and trunk roads in Wales were managed by the Ministry of Transport, later being taken on by the Welsh Office. The National Assembly for Wales took responsibility for devolved powers on 1 July 1999, as part of this process, transport was transferred from the Parliament of the United Kingdom to the National Assembly for Wales and with it responsibility for the trunk road network, including motorways. Responsibility for the management of highways in Wales is split between the Welsh Government and local highway agencies. The Welsh Government is responsible for trunk roads and motorways, whilst the 22 local authorities are responsible for all other highways.
In 2001 the Welsh Government reviewed the way in which trunk roads and motorways were being managed, and by September 2004, they had decided to reduce the number of trunk road agencies from eight down to three. The three new agencies including the South Wales Trunk Road Agency (SWTRA), which was later renamed the South Wales Trunk Road Agent.
The South Wales Trunk Road Agency (SWTRA) acts as Agent Highway Authority for the Welsh Government
As of April 2015, out of a total of 34,495 miles (55,514 km) of roads in Wales, 1,576 kilometres (979 mi) are trunk roads (including 133 kilometres (83 mi) of motorways and 350 kilometres (220 mi) of dual carriageway).