The M3 is a motorway in England, from Sunbury-on-Thames, Surrey, to Eastleigh, Hampshire; a distance of approximately 59 miles (95 km). The route includes the Aldershot Urban Area, Basingstoke, Winchester, and Southampton.

Sunbury-on-Thames is a town on the north bank of the River Thames in the Borough of Spelthorne, Surrey, England, 13 mi (21 km) southwest of central London. Historically part of the county of Middlesex, in 1965 Sunbury and other surrounding towns were initially intended to form part of the newly created county of Greater London, but were instead transferred to Surrey. Sunbury adjoins Feltham to the north, Hampton to the east, Ashford to the northwest and Shepperton to the southwest. Walton-on-Thames is to the south, on the opposite bank of the Thames.