Some train routes in England and Wales are running at almost double capacity, according to new research.
Rail passengers often have to stand on their daily commute
The 0759 Durham to Newcastle service tops the list, sometimes operating at 88% above capacity, according to environmental group Transport 2000.
Also highlighted were the 0718 Cambridge to London and 0753 Eccleston Park to Liverpool Lime Street, both often at 85% over capacity.
The Department for Transport has said it will add 1,000 carriages by 2014.
MOST OVERCROWDED ROUTES
Durham to Newcastle (0759) - 88%
Cambridge to London Liverpool Street (0718) - 85%
Eccleston Park to Liverpool Lime Street (0753) - 85%
Cardiff to Maesteg (1721) - 78%
Humphrey Park to Manchester Oxford Road (0814) - 75%
Morpeth to Newcastle (0800) - 58%
Barnsley to Leeds (0731) - 57%
Sheffield to Leeds (0714) - 53%
Sutton to Luton (1644) - 50%
Northampton to Birmingham New Street (0726) - 45%
Julia Thomas, Transport 2000's public transport campaigner, said: "It's very easy to blame rail operators for overcrowding problems, but actually a lot of it is down to the government's rail policy.
"They have issued 'no growth' franchises for the past 10 years and they've been promoting a policy of fare hikes to get people to travel off-peak, but passengers really don't have that much flexibility.
"In addition, the very short time periods covered by franchise agreements does not encourage any infrastructure investment by the rail operators."
The group said it is gathering evidence to send to Transport Secretary Douglas Alexander ahead of the government's expected major rail strategy report this summer.
A DfT spokesman said: "The government has acted and will continue to act to provide additional capacity.
"We've improved capacity in recent franchise contracts, and invested billions in major upgrades of the network.
"A fortnight ago we announced that we plan to add 1,000 extra carriages on the network - an increase of 10%. The first of the new trains will be put into use as soon as possible on the busiest parts of the network.
"And that is not the end of the story, as Transport 2000 are aware. Our rail strategy, to be published this summer, will give more details of how and where extra capacity will be created."