Motorists are facing diversions of about 12 miles (19.3km) for five to six weeks as bridge repairs are carried out in Conwy county.
Conwy council is repairing the bridge at Tal-y-Cafn, which links the A470 to the western side of the River Conwy.
The closest crossings of the river are at Conwy castle six miles (9.7km) north of the bridge, or at Llanrwst, seven miles (11.3km) south of the village.
The council said the bridge needs "essential repairs".
Work includes resurfacing, replacing joints and concrete and upgrading drainage.