Boris Johnson has unveiled plans for a new airport in the Thames Estuary that have been nicknamed Heathrow on Sea by some. Under the plans a new airport would be built on two Thames islands as an alternative to expanding the current airport at Heathrow. The airport would cost around £40 billion to build and initial reports have suggested it would serve Britain better than the planned Heathrow expansion. If it were to go ahead it could be built in eight years. The airport would be split in two with four runways split across two separate islands in the mouth of the Thames. Passengers would shuttle between the islands using a tunnel below the riverbed. Underwater turbines built into the ducts running through the island would generate nearly all of the airports electricity by harnessing the tides. The two terminals would then be served by a road and rail links and connected to Crossrail and the Channel tunnel rail link taking passengers into central London in around 35 minutes. Flights would take off and land over water and so would cause little disturbance to nearby towns.