|Frequency||About every 10-20 minutes|
|Length||8 miles (13 km)|
|Vehicle(s)||Volvo B7TL 10m /
Alexander ALX400 or Plaxton President
|† peak vehicle requirement|
for London •
Route 120 was one of the routes the new London Transport took over from London General in 1933. It ran daily from Hounslow Heath (Barrack Road) to Hayes Station via Staines Road, Lampton Road, Heston Road, Norwood Road, King Street, The Green, South Road, Uxbridge Road, and Coldharbour Lane. It was operated with ST buses from Hounslow (AV) Garage (Monday to Saturday) and Hanwell (HW) Garage (Saturdays and Sundays). Between Hounslow an Southall it followed the route it still has 75 years later.
On 4 March 1936 the 120 was withdrawn between Hounslow Heath and Southall, being replaced by new route 105, which ran between Shepherds Bush and Hounslow Heath via Western Avenue and Greenford. Although it no longer went through Hounslow, route 120 was operated by just AV throughout the week, until 13 April 1938, when HW took over on Monday to Saturday. AV's involvement ceased altogether (for 49 years) on 4 May 1938, when the Sunday service was withdrawn.
On 12 October 1938 the 120 was reinstated between Southall and Hounslow Heath on Monday to Saturday, as 105 was curtailed at Southall and extended beyond Shepherds Bush to Wandsworth Bridge. Route 105 continued to provide the Sunday service to Hounslow Heath until 18 October 1939, when it was curtailed at Southall and replaced by route 120, running between Hounslow Heath and Southall (Town Hall). The evening service between Southall and Hayes was withdrawn on 6 December 1939, but was reinstated on 15 May 1940. On 29 June 1941 the route was extended to Hayes on Sundays, but withdrawn again over this section on 1 November 1942.
Sometime between 1945 and 1949 a new route 120A was introduced, running from Hounslow Heath to Southall, and thence via Lady Margaret Road and Ruislip Road to Greenford (Civil Engineer). Route 120 continued on weekdays but was withdrawn on Sundays.
On 12 October 1955 route 120A was withdrawn on Mon-Friday and Sunday, being replaced by new route 232 and by the reinstatement on Sundays of route 120 between Hounslow Heath and Southall. On 16 October 1957 the 120A was withdrawn on Saturdays.
On 26 November 1958 the 120 was withdrawn between Southall and Hayes on Saturdays. From 9 November 1960 the Monday-Friday extension to Hayes was withdrawn apart from a some peak hour journeys 0.75 miles along Uxbridge Road to the junction with Delamere Road. The section to Hayes was replaced by new route 207A as part of the trolleybus replacement programme for trolleybus route 607. The Delamere Road journeys were withdrawn on 8 May 1963.
From 3 October 1965 route 120 was extended on Monday to Friday and Saturday from Southall via Lady Margaret Road, Somerset Road, Allenby Road, Ruislip Road and Greenford Road to Greenford Station. The Greenford terminus was changed to Bridge Park on 14 October 1976. On 30 June 1979 the Sunday afternoon service was extended to Greenford Broadway. On 4 December 1982 the Greenford terminus Mon-Friday peaks and Saturday daytime reverted to Greenford Station.
On 21 November 1987 the route was extended at the Hounslow Heath end Monday to Saturday daytime in a loop via Martindale Road, Beavers Lane, Salisbury Road, Green Lane, and Staines Road to Hounslow Heath, and then via Staines Road and High Street to Hounslow Bus Garage. Operation was transferred to AV.
On 28 April 1990 the route was changed in Hounslow, to run from Lampton Road via High Street directly to the Bus Station, thus severing the long connexion with Hounslow Heath, as well as the more recent loop via Beavers Estate.
The route was extended from Southall to Northolt Station, to replace the discounted route 232 on 24 March 1993.
Southall (HW) closed in 1986 and the allocation was transferred to Hanwell (HL) for a short time.
Allocation was transferred to Hounslow (AV) garage in 1987, using Metrobuses. The 120 was one of the five routes in London to gain the first fully accessible low-floor single deckers in 1994: Dennis Lance SLFs with Wright Pathfinder bodywork.
In 2000, when patronage was increasing the frequency was increased, and brand new Volvo B7TL 10m / Alexander ALX400 (VA) and Plaxton President (VP) were bought to convert the 120 and fellow London United route H32 into low-floor.
In December 2007, buses were leased from First London for use on the route to allow for conversion to ibus.
According to EPTUG, route 120 has become the most complained about bus route in Ealing. 'Extensive monitoring was carried out confirming that erratic time-keeping and serious overcrowding were in fact commonplace.' 
Route departing Northolt
Route departing Hounslow