The Highways A303 consultation document:
"Better access: the A303 is a difficult road to cross on foot. Surveys show that many visitors do not venture into the southern half of the WHS at the moment. Removing the road would make it much easier for people to explore more of the WHS and discover other important monuments by being able to roam freely and safely between different parts of this unique landscape."
Heather Sebire, Senior Property Curator for English Heritage in Antiquity Journal
"To the south of the monument, the proposed A303 road scheme has the potential to transform the World Heritage Site landscape further. The long-term vision for this remarkable and unique ancient site is the removal of the busy current surface road, as it will allow Stonehenge to be experienced without the intrusive drone of traffic and glare of headlights.
Visitors will be able to look out to the many burial mounds associated with Stonehenge from the monument, without the constant blur of cars and lorries obscuring the view. If the proposed tunnel scheme, and associated infrastructure, is designed well and located sensitively, the Outstanding Universal Value of the World Heritage Site and its assets could be greatly enhanced whilst simultaneously improving the setting of Stonehenge itself and people’s experience of it".
Note the difference between encouraging people to explore the landscape and the English Heritage's "Visitors will be able to look out..improving the setting of Stonehenge itself and people’s experience of it".
Guess they don't want people to leave their pay to enter area.