A growing number of UK companies is mandating or encouraging staff to use trains for short haul domestic trips.
BT, one of the UK's biggest companies, and the BBC, which is moving part of its operation from London to Manchester, are both understood to be among those urging staff to go by train rather than fly.
The routes in question are mainly ones like Liverpool, Manchester and Newcastle to London which, because of the UK's improved rail services, are now seen increasingly as train journeys.
Adrian Watts, sales and distribution director at TheTrainline, said: "We have seen an increasing number of corporates changing their travel policy to encourage employees to travel by rail and not by air on all domestic trips."
Part of the reason is the ecological factor but one travel manager said that with advanced bookings, going by train could be less expensive than flying.
TheTrainline, an online booking engine widely used by UK corporates, launched a carbon emissions reporting service in February to help businesses monitor carbon emissions caused by travel.
Mr Watts said: "We believe that this product will become industry standard. We expect 25% of our clients to have opted in by the end of this year."
One company which is encouraging its travellers to go by train is worldwide real estate and construction consultants EC Harris which has 22 offices throughout Britain.
Ms Carla Mandviwala, its group procurement manager, said the company made hundreds of journeys from cities like Manchester, Liverpool, Leeds and Newcastle each week.
"We used to use low cost airlines but in the last 12 months we have tried to discourage people from taking short journeys by plane," she said.
The project was helped by Virgin Trains' then offer of free first class journeys for passengers who could produce a boarding card for a plane trip.
But Ms Mandviwala said staff got to like the first class travel and were happy to use trains. If staff got reductions by booking in advance, they could continue to go first class.
By booking in advance, she said it has also got the average price of a ticket down.
"The decision to encourage trains was a mixture of "green" reasons and costs," Ms Mandviwala said.
She said agents were charging a flat transaction fee whether the plane journey was from London to Hong Kong or London to Newcastle. "Sometimes the cost of the fee was the same as the cost of the flight," she said.
Booking through engines like TheTrainline cost 9% commission and this was included in the fare.
“We have not calculated out savings but they are substantial,” Ms Mandviwala said.
EC Harris is now considering whether to extend the "train" policy further afield to include journeys from cities like Glasgow and Edinburgh to London although Ms Mandviwala said the time factor would play a crucial role in any decision.
*The switch comes as Eurostar has also launched an initiative to make rail travel "greener". Richard Brown, ceo of the high speed service from London to the continent, said it aimed to cut C02 emissions by 25% per passenger by 2012.
He said this would be achieved by cutting power consumption by its trains, improving use of train capacity and using more electricity from lower emission generators. Mr Brown said that before these now moves, travelling by train was already ten times "greener" than flying.