Newly published research shows the number of flights to Heathrow could be cut by 100,000 a year if people took the train instead.
If travellers used rail services to get to destinations like Paris and Amsterdam, Heathrow Airport would have less traffic.
Data for the research was gathered by the anti-airport expansion group Hacan Clearskies and published to coincide with a recent protest against short haul flights.
The research shows Paris is Heathrow's top destination, with 60 flights a day and Amsterdam, with 50 flights a day was second place. Brussels, which is just over two hours from London by train, has 30 daily flights.
In total there are about 100,000 flights each year serving cities with good rail connections: Edinburgh, Glasgow, Leeds, Newcastle, Manchester, Brussels, Paris, Amsterdam, Rotterdam and Middlesborough.
Hacan chairman John Stewart said: "The purpose of Heathrow should be to link London up with long-haul destinations, particularly the United States and the growing economies of China and India.
"These short-haul flights are simply clogging up the airport. Even if their numbers could just be halved, there would be no need to build a third runway or get rid of runway alternation."
The campaign group is calling for Government action to cut the number of short-haul flights at the airport.
The report, titled Short-Haul Flights: Clogging up Heathrow's Runways, recommends increasing Air Passenger Duty on all short-haul flights, especially for those destinations with good rail alternatives.
The Hacan chairman said there should also be emissions charges on aircraft to make the aviation industry pay the full cost of the environmental damage it causes.
Visit hacan.org.uk and click on Read the Hacan Research' for more information on the report.
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