The A55 is one of the busiest in north Wales

The project on the A55 at Penmaenbach near Conwy will take six months and eventually restore the road to dual carriageway.

The eastbound road, which runs alongside the London to Holyhead railway line, was reduced from two lanes to one shortly after the Selby train crash.

It was feared the walls were not strong enough to prevent traffic crashing on to the railway line below if there was an accident.

The Welsh Assembly Government has awarded �1.5m contract for the strengthening work.

While work is continuing for the next six months, drivers face a contraflow with only one lane of traffic in both directions.

In February, it was revealed the Welsh assembly was to carry out a study of the A55, which includes considering the possibility of building of a second tunnel for the Penmaenbach stretch of the coastal route.

The project involving the headland road and other sections of the dual carriageway was revealed in a letter written by the then Welsh Environment Minister, Sue Essex.