Arup and Atkins have been jointly awarded the contract to devise plans for the A303 Stonehenge Tunnel project.
The companies will draw up detailed features of the plan, which include a tunnel that will remove the sound of cars from the vicinity of the ancient stone circle in Wiltshire.
After drawing up plans for public consultation, the firms will produce a preferred option for the secretary of state to approve.
If all goes to plan, work could begin by 2020, creating hundreds of construction jobs across the south-west of England.
Global highways business leader at Arup Tony Marshall said: "By working collaboratively we can produce a transport solution that is sensitive to an area that is of immense cultural and environmental importance."
The idea of a tunnel has been supported by the National Trust and English heritage, who own and manage the land around the 5,000-year-old structure.
Recent archaeological digs have found a number of other traces of ancient settlements and monuments in the area surrounding the circle.
