Communications within Wales are influenced by the topography and the mountainous nature of the country: the main rail and road routes between South and North Wales loop to the east and pass largely through England. The only motorway corridor in Wales is the M4 motorway from London to South Wales, entering the country over the Second Severn Crossing, passing close to Newport, Cardiff and Swansea and extending as far west as the Pont Abraham services before continuing northwest as the A48 to Carmarthen. The M48 motorway parallels the M4 between Aust and Magor via Chepstow. The A40 is a major trunk road connecting London to Fishguard via Brecon and Carmarthen. The A487 coast road links Cardigan with Aberystwyth, and the A44 links Aberystwyth with Rhayader, Leominster and Worcester. The main trunk road in North Wales is the A55 dual carriageway road from Chester past St Asaph and Abergele, continuing along the coast to Bangor, crossing Anglesey and terminating at Holyhead.