Traffic taking the A55 into England must negotiate a tight 270 degree speed-limited single lane curve to climb up and over the A55/A494 at Ewloe loops.

Plans to upgrade the A494 between this junction at Ewloe and Queensferry were rejected by the Welsh Government on 26 March 2008 due to their scale.

This section of road is notorious for poor weather conditions including fog, ice and snow in winter months.

Unlike other sections of the A55 that have National Speed Limit (NSL) signage and are accessible to all motor vehicles, motorway restrictions are enforced on these two stretches of road (therefore no pedestrians, learner drivers, etc.)

[5] The crossing of the estuary of the River Conwy is by means of an immersed tube tunnel, the first of its kind constructed in the United Kingdom.

[7] The decision to construct an immersed tube tunnel bypass followed an extensive public consultation, named the Collcon Feasibility Study.

The 3 million tonnes of silt and mud extracted to create the trench in which the tunnel sections sat, were vacuumed to one side of the construction site, as to let them drift down river would have harmed the large mussel fishing beds downstream.

The silt was deposited upstream of the bridge at Conwy which created a large new area of low-lying land which was subsequently given to the RSPB for a wildlife preserve.

This new route, carrying traffic in both directions, relieved the original coach road built by Telford in the early 19th century.

Originally at the western end (Llanfairfechan) of the modern Pen-y-Clip tunnel, access was only allowed in an easterly direction because travelling the other way would mean heading the wrong way up the eastbound carriageway.

For instance the eastbound carriageway at Penmaenbach is subject to a 30 mph (50 km/h) speed limit due to sharp curves and double white lines nominally preclude lane changing.

The Bangor bypass, in which the road previously terminated and became the A5 regains high standards and is such through the Anglesey section, bar the Britannia Bridge, which is a single carriageway deck above the North Wales Coast railway over the Menai Strait.

This 20 mile (32 km) section from the end of the Llanfairpwll bypass to Holyhead Harbour was constructed as Private Finance Initiative scheme where the builders, a Carillion / John Laing joint venture, earn a shadow toll based on usage and lane availability.

The approach to Holyhead required major work with a new section over the sea paralleling the Stanley Embankment that carries the original A5 and the North Wales Coast railway.

It involves constructing a new road to the north of the dual carriageway for general use including cycleway and farm access.

This allowed the closure of 8 central reservation gaps used by slow moving agricultural vehicles which caused safety concerns with the volume and speed of traffic on the dual carriageway.

[13] In June 2021 the Welsh Government decided to review all road schemes whilst looking at public transport alternatives.

[14] In September 2021 the Welsh Government announced an expansion of their plans for the North Wales Metro that may impact this road scheme.

In November 2012, the Welsh Government published two more detailed studies looking at options to improve transport in the North East Wales and the A55 / A494 areas.