Wiltshire Police are urging anyone celebrating the summer solstice at Stonehenge between 7pm today and 8am tomorrow to get there by public transport.
Supt Gavin Williams said: "As solstice occurs at the start of the weekend this year, we anticipate higher numbers of people attending and therefore more vehicles in the area.
"Parking is limited at the site and we advise people to use public transport such as the Salisbury Solstice bus service wherever possible to avoid disappointment.
"Vehicles will be turned away once the available space has been filled and any vehicles parked illegally will be dealt with appropriately.
"The surrounding roads, in particular the A303, A360 and A345 are likely to be extremely busy with long delays possible.
"We are working closely with English Heritage and the Highways department on this issue but would advise non solstice traffic to avoid the area if possible.
"English Heritage have conditions of entry to the event and we ask that those attending adhere to these conditions.
"Our priority is to ensure that Solstice 2014 is a safe and peaceful event and we hope that everyone attending enjoys the celebrations."
Access to the stones and the car park is free of charge between 7pm today until 8am tomorrow, subject to conditions of entry which are published on the English Heritage website here
Information about the Salisbury Reds Summer Solstice bus service is at http://www.salisburyreds.co.uk/summer-solstice/