The Highways Agency is warning drivers to avoid the A303 around Stonehenge on Friday and Saturday morning during the summer solstice celebrations.
Around 35,000 people are expected to attend the celebrations, which take place at sunrise on Saturday.
Stonehenge will be open for the celebrations between 7pm on Friday to 8am on Saturday.
Those attending are being encouraged to use a frequent special bus service running from Salisbury throughout the Friday night and into the next day to avoid delays reaching Stonehenge.
Road users travelling by Stonehenge on the A303 are are advised to plan their journeys in advance and allow longer to reach their destinations.
Information about Salisbury Reds Summer Solstice bus service is at www.salisburyreds.co.uk/summer-solstice/ and the Highways Agency information line is on 0300 123 5000.