Motorists have been warned to expect traffic delays from tomorrow (Thursday) while Sonisphere music festival takes place.

The event is being held in the grounds of Knebworth House and will see festival-goers begin arriving today ahead of three days of music which kicks off on Friday.

The rock festival typically attracts more than 50,000 people and organisers are expecting similar numbers for this year’s show, which will see headliners The Prodigy, Iron Maiden and Metallica all perform.

Those attending will need to use junction 7 of the the A1(M) at Stevenage to access the site, with motorists unable to head north or south from the junction from 5am today until 3pm on Monday.

Northbound traffic can use junction 7 to left turn into the venue, while those travelling south should leave the motorway at junction 8 for Stevenage and go along the A602 Hitchin Road, A1072 Gunnels Wood Road and A602 Broadhall Way.

Westbound traffic should use the A602 to get to the turning for the venue at the roundabout for junction 7 of the A1(M) and those heading eastbound should use the A602 to A1(M) at junction 8 then follow the same route as southbound traffic.

To leave the venue motorists should head passed the Hotel Novotel Stevenage and onto the roundabout for the A1(M) at junction 7 to head southbound or follow signs for junction 8 to head north.

Alternatively, drivers can leave the site through Deer Gate and go onto Old Knebworth Lane, then the B197 London Road and follow signs to either Stevenage A1(M) junction.

Extra late-night trains are also being laid on by First Capital Connect, with festival-goers told to travel to Stevenage Railway Station – where there will be a shuttle bus service – and not Knebworth.

Superintendent Simon Hawkins from Hertfordshire Constabulary has issued a warning for both those attending Sonisphere and motorists in general.

He said: “We want people to enjoy the event safely and whilst we know crime prevention won’t be the first thing people think of, we would ask you take some simple steps to protect themselves – emptying and locking your vehicles and making use of the on-site lockers for your valuables.

“There will be a police presence at the festival and police cadets will be around before festival-goers enter the site to offer security marking and give out some crime prevention advice so please do stop and speak with them.

“I would also like to remind drivers using the A1(M) and roads surrounding the site that they may face some delays. We would ask them to familiarise themselves with the traffic information and thank them for their patience.”

The weekend will also see performances from acts such as Gary Numan, Frank Turner and Limp Bizkit. Novelty acts such as Chas and Dave and pirate rock stars Alestorm will also play sets.

Sonisphere day tickets are available for tomorrow priced at £55 plus a £8.25 booking fee, while Saturday and Sunday day tickets are both priced at £75 plus a £9.75 booking fee. Visit www.sonisphere.co.uk for more information.