The A55, also known as the North Wales Expressway, is a major road in Britain. Its entire length is a dual carriageway primary route , with the exception of the point where it crosses the Britannia Bridge over the Menai Strait.

It runs west from its junction with the M53 motorway near Chester, crossing the Welsh border and the River Dee, Wales before passing north of Buckley and south Holywell. Passing close to Northop the road climbs up onto the Denbigh moors on the flanks of Halkyn Mountain. This section of road is notorious for poor weather conditions including fog, ice and snow in winter months. In fine weather this section provides extensive views over the Dee estuary to Liverpool and beyond. The descent towards St Asaph is down Rhuallt hill. The road bypasses St Asaph and runs along the North Wales coast passing Abergele, Colwyn Bay, Conwy, Penmaenmawr and Llanfairfechan before heading onto the island of Anglesey, where it ends in Holyhead, from where ferries connect with the Irish port of Dún Laoghaire.

The coastal section involved major civil engineering works, with two hard rock tunnels passing through the cliffs in two places.

The crossing of the estuary of the River Conwy is by means of a tunnel that was constructed as pre-formed concrete sections and then floated into position over a pre-prepared trench in the bed of the estuary. The use of a tunnel followed an extensive public consultation which ruled out another birdge on aesthetic ground since it would have damaged the view of the world heritage site Conwy Castle and the two bridges by Robert Stephenson and Thomas Telford. Because of the valuable fishery in the river and also because of the past history of heavy metal mining in the catchment of the river, extensive ecological assements were made both prior to the construction of the tunnel and subsequently which finally concluded that no significant environmental damage had been caused.

Part of the route around Colwyn Bay has restrictions on pedestrian and other traffic similar to that on a motorway, although parts of this stretch have a 50 mph speed limit.