Originally the London to Portsmouth road passed through numerous towns and villages - including Kingston-upon-Thames, Esher, Guildford, Godalming, Petersfield and Havant, but a programme of road improvements starting in the 1930's has transformed the road so that is now predominantly a two or three lane dual carriageway.
All the main towns have been by-passed, but a short stretch of single carriageway road remains in the vicinity of Hindhead and the Devil's Punchbowl beauty spot, about 8 miles 13 km) south-west of Guildford. A 1.9 km tunnel under Hindhead Common is planned, subject to a Public Enquiry, with construction timetabled for 2005-2009.
In London the South Circular Road merges with the A3 for a while.
The road is heavily used by commuters and long queues build up at Hindhead, particularly during the morning peak hours.