Rail commuters have been promised an extra 1,000 train carriages by 2014 in a bid to tackle overcrowding.
Rail passengers often have to stand on their daily commute
The commitment was made by Transport Secretary Douglas Alexander in a speech at a rail conference in London.
He said the new carriages were "an important first step" in tackling overcrowding on a network with more than one billion journeys a year.
Most of the new carriages are expected to go on the jammed routes serving London and south-east England.
Passenger Focus and the Association of Train Operating Companies both welcomed the announcement.
The government will pay for the new carriages then lease them to the train companies at a cost of about £130 million a year.
As well as relieving the problems in south-east England, crowded cities in the rest of England and Wales are also expected to benefit.
Last year, there was a 10% rise in the numbers of people taking the train and overcrowding has rapidly become the number-one problem facing the railways.
Train companies have been making dire warnings about the future, and passengers are being told they will have to stand more often.
ATOC director general George Muir said an extra 1,000 carriages would make "a lot of difference" but warned that any extra capacity would quickly be used up.
"The railways are proving enormously successful. There's an enormous growth in passenger numbers and, if we don't put more carriages on, conditions are going to get even more intolerable than they are now," he told BBC News.
"It's going to be a little bit neck and neck to keep the capacity and the growth alongside each other."
But work would need to be undertaken on existing platforms to cope with longer trains, he added.
Mr Alexander said longer-term planning was also being done.
"We are now generating increased revenues from the larger number of people using Britain's railways," he said.
"In the past we had to spend that money on some basic investment dealing with botched privatisation, now we are able to turn that investment towards the kind of capacity improvements people have been looking for."
This summer the government would "take a 30-year view" to examine the capacity challenges ahead, he added.
Shadow transport secretary Chris Grayling said the Conservatives supported the idea of longer trains, but added that these had been promised five years ago in the government's 10-year plan for transport.
"The problem is nothing is going to happen for seven more years, at a time when overcrowding is already endemic," he said.
"This is just another 'jam tomorrow' announcement from the government."
Liberal Democrat transport spokesman Alistair Carmichael said any measures to relieve overcrowding would be welcomed by passengers.
But he said it would be better to allow Network Rail to own the trains and operate as a rolling stock leasing company to "bring better integration between track and train and ensure less money is drained out of the system".
Gerry Doherty, general secretary of the transport union TSSA, also supported a Network Rail leasing plan.
Later this year the government will publish a wider strategy to improve the capacity of the rail network.