SL9
London SovereignBYD Alexander Dennis Enviro400EV atHeathrow Central bus station
Overview
Operator	London Sovereign (First Bus London)
Garage	Harrow
Vehicle	BYD Alexander Dennis Enviro400EV
Began service	7th December 2019 (renumbered SL9 on 26 August 2023)
Former operator	Metroline
Night-time	N140
Route
Start	Heathrow Central bus station
Via	Harlington Hayes Yeading Northolt South Harrow
End	Harrow bus station
Service
Level	Daily
Route map Legend Route SL9  N140  140 toHarrow Weald bus garage Harrow bus station  SL9  South Harrow station Northolt Park station Northolt station Yeading White Hart Roundabout Yeading Dilston Close Yeading Willow Tree Lane Hayes the Grapes  278 toRuislip High Street Hayes & Harlington station  140  Harlington High Street Harlington Corner Heathrow Central bus station  N140  SL9  278  This diagram: view talk edit ← {{{previous_line}}}  {{{system_nav}}}  {{{next_line}}} →

London Buses route SL9, formerlyLondon Buses route X140, is aTransport for London contractedSuperloop express bus route inLondon, England. Running betweenHeathrow Central andHarrow bus stations, it is operated byFirst Bus London subsidiaryLondon Sovereign.

The route commenced on 7 December 2019, originally numbered X140, as part of a reorganisation of routes in the lead up to the opening of theElizabeth line. Route X140 was introduced as a limited stop service betweenHarrow andHeathrow Central bus stations and as a partial replacement for the all stopsroute 140, which was withdrawn between Hayes & Harlington and Heathrow at the same time.^[1][2] Route X140 was initially operated byMetroline.

Upon being put out to tender, on 4 September 2021 route X140 was taken over byLondon Sovereign'sHarrow bus garage.^[3][4] However, due to delays in the delivery of newBYD Alexander Dennis Enviro400EVs and the refurbishment of theWright SRM bodiedVolvo B5LHs for the route, London Sovereign initially operated it withWright Gemini 3 bodiedVolvo B5LHs.^[5]

On 26 August 2023, route X140 was renumbered SL9, becoming part of theSuperloop express bus network.^[6][7][8][9]

On 28 February 2025, the route passed fromLondon Sovereign toFirst Bus London following the acquisition ofRATP Dev Transit London byFirstGroup.^[10]

Route SL9 operates via these primary locations:^[11]

• Heathrow Central bus station
• Harlington
• Hayes & Harlington station
• Hayes
• Yeading
• Northolt station
• Northolt Park station
• South Harrow station
• Harrow bus station

The route operates at a frequency of a bus every 12 minutes on weekdays and Saturdays and a bus every 15 minutes on Sundays.^[12] Between the hours of 23:00 and 07:00, the route is covered by an all stops night service, numbered N140, running every 30 minutes betweenHarrow Weald bus garage andHeathrow Central bus station.^[13]

Media related toLondon Buses route SL9 at Wikimedia Commons

• Bus routes in London
• Buses serving Heathrow Airport
• Transport in the London Borough of Harrow
• Transport in the London Borough of Hillingdon
• London Superloop

• Articles with short description
• Short description matches Wikidata
• Commons category link from Wikidata