London, Manchester and Bristol may all have reached “saturation point” when it comes to traffic, according to analysis by a campaign group.
Greener Journeys also found that traffic speeds in Reading and Slough are stalling at around the 10mph mark.
Professor David Begg, of Plymouth University and former chairman of the Government’s Commission for Integrated Transport, said it is now more important than ever to try to change travel behaviour.
“If we don't try to influence people's travel choices, it will mean that we all have no choice but to sit in ever increasing traffic jams,” he said.
He added that congestion was becoming a disease in many UK cities, which could have a devastating effect on the nation’s buses in particular.
Prof Begg claimed that bus journey times are increasing by 10% per decade.
If this trend continues the future of bus travel would also be under threat as passenger numbers will drop by between 10% and 14% every decade.
Some bus routes in the capital have been reduced to “walking pace”, the report showed.
The report comes after the RAC recently urged new London mayor Sadiq Khan to implement measures to help combat congestion in the capital, likening the pace of traffic in some parts of London as “slower than horse-drawn carts”.
The findings from Greener Journeys come after separate research which showed the number of cars on Britain’s roads is at a record high.
The Department for Transport figures revealed that in 2015 the UK had around 30 million cars in use, an increase of some 43% on the total from 1995.
Motorway traffic was also found to have shot up by 44% over the same 20-year period.
Claire Haigh, chief executive of Greener Journeys, said: “This report highlights the shocking growth in congestion blighting major cities across Britain, and particularly the heavy toll it is taking on the bus sector which is vital to our economy and our society.”