Traffic has been stopped from using a section of the A344 next to the stones, in Wiltshire. It will now be dug up and grassed over.
The road has been closed in both directions between Airman's Cross and the A303 at Stonehenge Fork.
Drivers are advised to follow the diversion via the A360 Longbarrow roundabout.
English Heritage wanted to close the road to "restore the dignity" of the World Heritage Site.
Peter Carson, from English Heritage, said the move would also improve the experience for visitors.
He said: "The stone circle and the avenue that links it with the landscape will at last be reunited, which means people can explore the wider landscape and see the wonderful archaeological features contained within."
Work to permanently close a main road running alongside Stonehenge has started.