Heavy rain which left a road unfit for vehicles led to huge tailbacks around parts of Preston.
The traffic lights controlling vehicles passing the works on the roundabout at the junction of Eastway and Andertons Way, Fulwood, were left on during the Tuesday evening rush hour.
A spokesman for Lancashire County Council said heavy rain had left workmen unable to restore the road to a suitable standard in time to allow vehicles to use it.
The delays lead to huge tailbacks around Eastway which spread onto the nearby North Preston Employment Area and up to the roundabout at Broughton, which accesses the M6 and M55 motorways.
He said: “Towards the end of the day, the heavy rainfall washed out a trench which meant we were unable to restore the road before the rush hour started.
“We are sorry for the inconvenience made to people’s journeys, the project we are working on to widen roundabouts and increase capacity will help prevent delays in future.”
Motorists reported being held up in jams of more than an hour as hundreds of people attempted to navigate the queues caused by the lights.