Drivers are being warned about possible delays in the area from tomorrow (Thursday) until Monday as tens of thousands of rock fans descend on Comet country for this weekend’s Sonisphere festival.

Herts Police put out the warning ahead of the three day metal festival in the grounds of Knebworth House where 60,000 fans are expected.

Journeys will be affected by the closure of the northbound on and southbound off slip roads at Junction 7 of the A1M from 6am tommorow until noon on Monday.

A police spokesman said festival traffic approaching from the south will be directed to leave the motorway at Junction 7. Those approaching from the north will be directed to leave the motorway at Junction 8 and take the A602 towards Hitchin before joining the B656 southbound. Local traffic will be unable to leave the motorway at Junction 7.

Shuttle busses will be in place at Stevenage Railway Station to take festival rail passengers to and from the estate.

Superintendent Simon Hawkins, in charge of planning for the festival, said: “We are in for a very busy weekend as not only will thousands of people be heading for Knebworth Park for Sonisphere, but thousands will also be heading to Hitchin for Rhythms of the World.

“We appreciate that this will have some impact on the local community and may cause delays and I would ask residents to please bear with us throughout the weekend and where possible take alternative routes.

“The A1M junction 7 is being closed to ensure the safety of those walking to the site. This year the closure comes into place on the Thursday and we hope this will save any confusion for people who regularly use the road. We have also put in place a one-way-system this year to help the flow of the traffic.

“We have been working with the event organisers and the highway authorities for months to make improvements on the road plans from last year and traffic will be monitored during the course of the weekend.”

Festival organiser Stuart Galbraith said the run up to the event has gone smoothly.

“It’s looking very good indeed there on site,” he said. “We are well ahead of the programme. The weather has been good during the build up.

“We work very hard indeed with the police and the council and try to minimise any inconvenience.”

He added that the festival gives a boost to the local economy: “The festival brings in six to eight million to the local community, in terms of hotels, petrol stations, shops. You only have to go into Tesco during the festival to see that.

Having the ‘big four’ thrash metal originators – Anthrax, Metallica, Slayer and Megadeth playing on the opening night was a huge coup, he said.

“They’ve never played in the UK together – to have them on the same stage is fantastic. Having the big four is certainly something very special. I have to say the four of them one after the other is very good.

“There are so many other highlights. Bill Bailey live. Biffy Clyro will surprise an awful lot of people. I saw them the other day, they are really, really looking forward to it.

“We are broadening Sonisphere out – not just thrash and metal, so we have Mars Volta and Bad Religion.”

The festival is set to take place again next year, with plans already underway, he added.