People using public transport face a "daily trauma" and are forced to travel in "intolerable conditions", according to a House of Commons report on overcrowding.
The committee says overcrowding is likely to get worse
The report said that failing to take the issue seriously was "tantamount to waiting for a tragedy to occur".
The influential cross-party transport committee called for "immediate and urgent plans" to improve the situation.
It took evidence from travellers who routinely found themselves subjected to overcrowding that was "not simply uncomfortable, but positively frightening".
"Improving the reliability of services, whether bus, underground, tram or rail, is a key part of this, but will not
be enough," the committee, chaired by Labour backbench MP Gwyneth Dunwoody, found.
KEY REPORT FINDINGS
Overcrowding will get worse
14% of people use public transport
In inner London the figure is 42%
In central London it is 80%
In London delays cost £230m at least
In Yorkshire peak rail capacity is exceeded by 9%
The MPs said passengers were often unable to board vehicles.
"Managements which accept overcrowding as inevitable are not only short changing the travelling public, they are failing to run the system properly."
The report, entitled Overcrowding on Public Transport, said that the hardened traveller may have come to accept the problem.
Costs to business
But it is one area where there needs to be "huge improvements" if public transport use is to increase.
The committee quotes a report from Oxford Economic Forecasting which found that lost business due to overcrowding and delays cost the City of London about £230m a year.
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Tourism - worth £75bn to the UK economy - is another area which is likely to suffer if overcrowding during the high season is not addressed, the MPs concluded.
The report is also adamant that overcrowding is not just a south-east of England phenomenon.
A survey by the Rail Passenger Users Committee of north-western England found overcrowding on many routes, with the
Huddersfield to Manchester route being singled out as particularly bad.
Labour MP Gwyneth Dunwoody chaired the committee
London Underground also comes in for criticism.
The committee was told by the London Transport Users Committee that most passengers are forced to stand at peak times.
Some stations are regularly closed for short periods to handle peak flows and long intervals between trains can cause overcrowding - even at off-peak times, the report noted.
Representatives of London Underground Ltd told the committee that reliability had improved and was expected to improve still further.
But the committee said the Chancery Lane derailment and its aftermath had demonstrated the "fragility" of the Underground system, and the need for staff to be thoroughly trained to deal with such problems.
And, in a swipe at the government's policy of public private partnership of London Underground, the MPs concluded: "We are not convinced that the PPP will provide the improvements forecast."
The report suggests a range of possibilities to tackle the problem, including lengthening trains, changing
service frequencies and even simply communicating better with the public.
"Constant gross overcrowding should not be an acceptable fact of travelling
The committee thought overcrowding on buses was less of a problem than on trams or rail, as one vehicle was likely to be quickly followed by another
But bus overcrowding could be much reduced by greater use and enforcement of bus priority measures and better bus design, the MPs found.