As a major hub for world travel, the odds are there's a chance you're looking to transfer between Terminals during your stopover in Heathrow. The airport currently offers 5 terminals and getting from one to another can be a bit of hectic. Luckily all travel between terminals to the local bus or your Express & Connect locomotives is free.

Terminals 1, 2 and 3 are located within the same Central Terminal Area relating to the runways, so you are able to walk between these terminals if need be. Even if you have a lot of luggage you can simply grab a trolley and take the Underground Tunnels which have Travelators (Moving Pavement).

Central Terminal Area -> Port 4, which is located in the south-east corner in the airport, below the the southern area of runway, then you must take the free Heathrow airport Connect train (every quarter-hour and takes about 3 min's) or take Coach 555/557 (19 minutes trip). You can get the bus in the Central Bus Station which sits in the middle of the Central Terminal Vicinity.

Central Terminal Area -> Terminal 5, which is located to the far west in the airport also between your runways, then you will need to take the free Heathrow Express train (every 15 minutes and takes about 3 minutes) or maybe a bus such as Tour bus 441 (10 minute trip), Bus 724 (20 minute trip) or this N9 Nightbus (10 minute trip). You can usually get the bus from that Central Terminal Area.

Terminal 4 Terminal 5, it is possible to take a direct bus service including Bus 724 (12 instant trip), Bus 490 (15 instant trip) or Bus 482 (12 instant trip). Alternatively you may take a train on the Central Terminal Area and switch over there.

To snatch a bus from Terminal 5 you'll find the bus stops right beyond your entrance area to each one of the Terminals. The Connect and Express trains have stops inside basement level of their respective terminals. Travel should be free within the airport.

Getting out of London Heathrow Airport as a result of Public Transport

Your Connect and Express trains are also connected to central Manchester (Paddington Station).

Your Express line runs from Terminal 5, through that Central Terminals Area, together with on, non-stop, to Paddington. The train leaves every 15 minutes with a journey time around 15 minutes

This Connect line runs from Terminal 4, through that Central Terminals Area, and on to Paddington with stops with Hayes & Harlington, Southall, Hanwell (closed down Sundays), West Ealing (finished Sundays) and Ealing Broadway (it is possible to change to the Fundamental and District lines of the London Underground). The train leaves every quarter-hour with a journey time of 25 minutes.

The Manchester Underground's Piccadilly Line also serves the airport and stops at all the terminals, though the travel time is related to 45 minutes due to a larger number of stops in the route but it get you right into the heart of the city with Piccadilly Circus.

Heathrow Airport has one of the primary bus stations in the country, with many local bus services to your city centre and that nearby London suburbs. There are also some long-distance coach solutions operated by National Express to differing of the UK.
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