Delay to new Pont Briwet road bridge at Penrhyndeudraeth
A new £20m bridge over the Dwyryd estuary in Gwynedd will not open to traffic until next year.
Cars are having to make an eight-mile (12 km) detour along the A496 while the replacement Pont Briwet bridge at Penrhyndeudraeth is built.
The two-lane bridge was due to open in time for Christmas but complex pipe replacement work means it will now be spring 2015.
A parallel bridge carrying the Cambrian rail line will open next week.
This had also been delayed and had been due to open in the summer.
The original 154-year-old road and rail bridges closed in January after safety fears and the council had been confident the new bridge would be open to vehicles by December.
But Gwynedd council said contractors reported a "significant amount of work" was still to be completed, with problems including transferring a water main.
"We have always acknowledged that this is a complex engineering project and accept that problems will be encountered which cause delays but we know how disappointing it is for the local communities to have to travel on the alternative route for longer than was anticipated," said a spokesperson.