Heathrow Airport to upgrade M25 with new tunnel and bridges while keeping traffic flowing

London Heathrow Airport (LHR) has revealed how it will deliver a new tunnel and bridges on the M25 while keeping traffic flowing during the construction of a third runway. The future-proofed section of motorway will be built ‘offline’ on land 130 metres to the west of the current road, separating construction from daily commuters. Traffic will be switched to the new route using carefully planned overnight closures.

Once complete, motorists will benefit from a wider and safer stretch of motorway, fully funded by Heathrow. New link roads will separate passing M25 traffic from vehicles leaving and joining the M4, eliminating weaving movements and providing safer journeys.

Watch Heathrow Masterplan M25 realignment here:

Since the expansion proposals were submitted to the Government, the M25 has been one of the most common questions raised. Heathrow has developed a clear plan in consultation with National Highways to upgrade a key part of the UK’s road network. Alternative designs, including building over the M4 spur, were considered but dismissed for providing less capacity, creating more disruption, and requiring the demolition of thousands of homes.

The M4 spur also runs over a crucial rail tunnel carrying Heathrow Express and Elizabeth Line services. Building on this constrained stretch would have caused significant disruption to both road and rail users. Alternative runway locations would have been too short to accommodate all long-haul flights, according to Heathrow and several airlines.

Surface Access Director, Sophie Chapman, for Heathrow, said: “Heathrow expansion is a once in a generation opportunity to upgrade our connectivity in the air and on the ground. One of the legacies of our plan will be a 100% privately financed upgrade to one of the busiest stretches of the M25. We have a tested plan for building next to the current motorway that will keep motorists on the move during construction. We have already looked at the alternatives and they simply create more impacts for less benefits so we’re confident we have the best plan available.”

Heathrow submitted its proposals to Government this summer, setting out how its vision for expanding the UK’s Gateway to Growth is ready to deliver the economic growth the country needs. Building a runway over a motorway is not unprecedented and has been successfully completed at other airports including Frankfurt and Charles de Gaulle in Paris. Heathrow will continue to work closely with National Highways to finalise the details of its plans, ensuring the M25 upgrade supports safe and efficient travel during and after construction.

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