With a journey time of 15 minutes Heathrow Express is the fastest way to travel from London to Heathrow

Mott MacDonald was the lead designer for the high-speed rail link between Heathrow Airport and London’s Paddington Stat-ion, developed to provide specially commissioned trains in both directions with an express journey time of 15 minutes.

As the world’s busiest international airport, Heathrow currently handles 60 million passengers per year and over 30 million people have travelled on the Heathrow Express since its completion in 1998.

Heathrow Express trains utilise the existing fast tracks on the Great Western Main Line from Paddington. The 8.5km airport branch leaves the main line close to Stockley Bridge and swings southwards into twin tunnels which pass first under the M4 motorway and then under the airport runways to reach the passenger terminals.

The scheme included 10km of tunnels and two new stations, one serving Terminals 1 and 2 and the central terminal area of Terminal 3, the other Terminal 4.

Mott MacDonald’s role as lead designer for the project was expanded by commissions to design the trackwork and all mechanical and electrical installations (apart from signalling) including ventilation and emergency services.

Construction involved three different tunnelling methods. The 5.7m diameter running tunnels were shield driven with expanded concrete linings, while the 800m long portal structure was formed by cut-and-cover construction in a landfill area known to contain leachate, methane and other landfill gases. The 7.8m wide station platform tunnels, together with railway junctions and vent adits, were constructed using sprayed concrete lining (SCL) for primary support and in some cases for secondary lining.

In late 1994 the temporary lining to the station tunnels in the central terminal area collapsed, creating a significant set-back. Working as a single team with the contractor and the client, Mott MacDonald succeeded in recovering the situation to the extent that the initial estimate of 18 months’ delay was reduced to six months. We also developed a revised design for the central terminal area station at the original location — incorporating a 60m diameter cofferdam to encircle the majority of the tunnel collapse zone — and undertook detailed checking and re-design of SCL primary support for tunnels where appropriate.

The first station is approximately 27m deep beneath Heathrow’s central terminal area, with two platforms and a central concourse containing ticketing, information and other facilities all at the same level to allow easy movement. Each terminal has a dedicated route from the station concourse with a choice of high speed lifts or escalators. A cross-over enlargement and two turnout enlargements were provided for the extension to Terminal 5. Just recently completed, the extension takes the Heathrow Express rail link from the existing rail station at the central terminal area to the new rail station located beneath the new Terminal 5 building.