The key revisions included a new 2 miles tunnel at South Ruislip avoiding the Chiltern Line and mitigating the impact in the Ruislip area; realignment of the route and extension of the continuous tunnel, originally from the M25 to Amersham, to near Little Missenden; at Wendover and nearby South Heath extension to the green tunnels to reduce impact on local communities; an extension to the green tunnel beside Chipping Warden and Aston Le Walls; and realignment to avoid heritage sites around Edgcote.