From the Wikipedia page [1], which gives a full listing of the localities covered.
The London Traffic Area was established by the London Traffic Act 1924 in order to regulate the increasing amount of motor traffic in the London area. The LTA was abolished in 1965 on the establishment of the Greater London Council.
The Traffic Area extended for about 25 miles (40 kilometres) from Charing Cross in central London, and was thus much larger than the existing County of London or Metropolitan Police District. It included the whole of the County of London and Middlesex, much of Surrey and Hertfordshire, plus parts of Kent, Buckinghamshire, Berkshire and Essex. At its outer limits it included Harlow, Billericay, Gravesend, Sevenoaks, Reigate, Guildford, Slough, Amersham, Harpenden and Stevenage.
The London and Home Counties Traffic Advisory Committee was set up to make recommendations on regulating and controlling motor traffic in the LTA, and presented annual reports to parliament. The committee included members appointed by the Ministry of Transport and by the local authorities in the Traffic Area.
The LTA and the advisory committee were abolished by the London Government Act 1963. From 1965 the Greater London Council exercised the powers over traffic regulation, although its area was much smaller than the traffic area.