Motorists have faced delays of up to an hour after roadworks in Berkshire started.
Temporary traffic lights and a reduced speed limit are in force along part of the A4 in Theale to allow for improvement works.
The work, which includes resurfacing and safety improvements, is set to last for eight weeks.
West Berkshire council has apologised for the inconvenience but said an accident has made the delays longer.
Phil Spray, spokesman for the council, said: "We understand from the police there has been an accident on the A340 near Theale and they have closed the road there which has had a knock-on effect on the A4.
"It has meant there is greater traffic then we would expect."
The council said the work will provide a smoother surface for drivers and reduce traffic noise.