A public inquiry was held in 1995, and in 2002 the government granted permission to build the road.
[2] The tunnel itself was constructed using a cut and cover method, during which the hill was cut away and the concrete tunnel structure then put in place.
The hillside was then re-filled in over the top - see Bypass Construction Gallery.
The purpose of the tunnel at this position is to reduce the gradient of the road, and to preserve the visual line of the hills and provide crossing points for wildlife such as deer.
The chalk cuttings for the tunnel have become a haven for butterflies which are native to the area.