Weymouth's relief road is unlikely to open until March, Dorset County Council has confirmed.
The £87m road is being built to ease traffic during the Olympic 2012 sailing events, which will be held in Weymouth and Portland.
It had been due to open in December but the southern part of the route is still incomplete.
The northern section of the road is finished and contractors are planting shrubs along the verges.
The road had already been delayed until February but the council now admits it may not be ready until next month.
The hold-ups have been caused by exceptionally wet or cold weather at various stages of the construction process, the council said.
The Princess Royal "officially opened" the site in December.
Weymouth and Portland will host 400 international sailors at the 2012 Olympic and Paralympic Games.
The events are to be held at the Weymouth and Portland National Sailing Academy at Osprey Quay.