The M61 was closed for around 40 minutes in both directions south of Chorley this afternoon due to a "police incident."
Officers shut both north and south carriageways between junctions 6 (Chorley) and 8 (Horwich) at around 4.20pm.
Highways England reported the southbound carriageway was partially blocked due to a "concern for safety incident."
Traffic was held in both directions while the incident was successfully dealt with.
Officers were able to release traffic at around 5pm after the emergency was resolved.
Before traffic was released a spokesperson for Lancashire Police said: "Road closures are currently in place as we deal with a concern for safety incident between junctions 6 and 8 of the M61.
"We would ask motorists to avoid the area if possible and find alternative routes as traffic is already backing up in the area."
Within 20 minutes the incident caused queues back to Rivington Services on the northbound side and up to Botany Bay on the southbound.
And the hold-ups were getting worse as the main tea-time rush hour traffic joined an already congested motorway. At 5pm the southbound queue was back to Walton Summit.
At around 5pm a Highways England spokesperson said traffic had been released, but warned drivers: "Be aware, it will take time for the backlog to clear. Thank you for your patience."