The Highways Agency is advising drivers of delays on roads around Knebworth Park ahead of the Sonisphere music festival this weekend.
Thousands of people are due at the event and congestion is expected on the A1(M) and around Stevenage and Knebworth.
Drivers will need to use the A1(M) junction 7 to access the site, which is different to previous events at the location.
The northbound entry slip road and southbound exit slip roads on the A1(M) junction 7 are closed now until Monday 7th July.
Northbound motorists can use junction 7 and turn left into the venue. Non-festival traffic can access Stevenage as normal.
Westbound traffic should use the A602 into the venue via junction 7 of the A1(M)
Eastbound traffic should use the A602 to junction 8 and then follow signs for southbound traffic.
To leave the venue motorists should take the Novatel Road onto the A1(M0 junction 7 roundabout.