Customers reported gridlock outside a supermarket on Friday.
Shoppers at Sainsbury’s in Bamber Bridge said they were stuck in the car park for over an hour.
Bosses at South Ribble Council said the queues were caused by a road sweeper.
A spokesman said a lane of the A6 in each direction had been closed for road cleaning, which happened twice a year.
He said the cleaning coincided with the roadworks at Lostock Hall, and described the gridlock as a “one-off”.