London Buses route U4 is a Transport for London contracted bus route in London, England. Running between Uxbridge and Prologis Park, it is operated by Metroline.
Route U4 commenced operation on 27 May 1989 between Uxbridge Station and Hayes Bourne Avenue via Kingston Lane - Hillingdon Hospital - Goulds Green - Judge Heath Lane - Hayes - Station Road - Dawley Road. The route was operated by CentreWest from their Uxbridge (UX) garage using Alexander bodied Mercedes-Benz 811Ds. The route was introduced in order to replace the withdrawn section of Route 204 between Hillingdon Hospital and Hayes.
On 2 May 1998, the route was retained by CentreWest with Marshall Capital bodied Dennis Dart SLFs introduced.
On 24 January 2004, the route was converted to double deck operation using Plaxton President bodied Dennis Tridents.
On 29 September 2012, the route was extended from Hayes Bourne Avenue to Prologis Park.
On 7 March 2015, Alexander Dennis Enviro 400s were introduced.
In July 2015, the Plaxton President bodied Dennis Tridents were replaced by Plaxton President bodied Volvo B7TLs.
On 20 August 2016, the allocation was transferred to Hayes (HZ) garage.
On 11 February 2017, the allocation was transferred back to Uxbridge (UX) garage.
On 29 April 2017, the route was retained by Metroline.
In September 2017, the route was converted to full Alexander Dennis Enviro 400 operation.
- Uxbridge Bus Station
- Brunel University
- Hillingdon Hospital
- Hayes & Harlington Station
- Hayes Bourne Avenue
- Prologis Park