A crash involving three lorries has closed the M1 southbound near Northampton at lunchtime on Thursday (July 15).
Emergency services shut all lanes and and two between junction 16 and junction 15A following the smash.
The southbound entry slip has been closed to traffic trying to join the M1 southbound at junction 16.
Traffic is also crawling past the scene on the northbound side.
A Highways England spokesman said: "There is heavy congestion southbound for 7½ miles adding at least 50 minutes to normal journey times.
"Please allow extra time for your journey and pass the scene with caution."
The smash is having a knock-on effect for traffic on the A5, A43 and A428 as thousands begin heading towards Silverstone for this weekend's British Grand Prix.
Traffic is being diverted via the 'Hollow Square' diversion symbol using the A4500 Weedon Road, A5076 Upton Way, Danes Camp Way and the A5123 to J15A.