The RAC Foundation has warned that motorists face longer delays on Britain's roads because of more cars and lower transport infrastructure spending.
Its latest report predicts that four million more cars will be on the roads in the next 25 years.
While this will be welcome news for car dealers, it will lead to frustration for drivers, according to the RAC.
The report warns: "Ministers have not explained what plans they have to cope with the bleak picture painted by their own numbers".
Roads Minister Mike Penning said £4bn was earmarked for various projects, reported BBC News.