Heavy showers brought roads around Lancaster, Carnforth and Halton to a standstill during the morning rush hour.
Drivers were urged to take care as many roads flooded.
Witnesses said a car became stuck in water under the railway bridge on Torrisholme Road.
The A6 into Carnforth was also backed up as far as Bolton-le-Sands for a time and workers were seen trying to unblock the drain at the bottom of Foundry Lane in Halton.
Lancashire Fire and Rescue Service were called to the M6 after a car hit the central reservation between the Kendal and Carnforth junctions.
A crew from Silverdale responded to the incident, one mile before Burton Services.
Spokesman John Taylor said: “A person had got out of the car and was, fortunately, uninjured so the car was pushed onto the hard shoulder and checked to make sure it wasn’t going to burst into flames.
“It didn’t turn out to be a multiple car pile-up, thankfully.”
The Met Office said scattered showers were likely throughout the rest of the day, some of which could be thundery.