The government's 10-year plan for transport will fail to meet its central pledge to cut traffic congestion by 2010, the transport secretary, Alistair Darling, will admit next week.

Mr Darling, three months into his new job, has decided to make a clean breast of this latest delivery failure as part of a "progress report" on the plan. He has told colleagues that he expects to take a big political hit over the admission.

Road users will be infuriated that jams and delays are not now expected to be reduced in this decade. The announcement will also add to the impression that the government is failing to deliver on its major public service targets.

The deputy prime minister, John Prescott, promised in 2000 that the plan would cut congestion on inter-urban trunk roads by 5% by 2010, compared with a forecast growth of 28% if the 10-year plan was not implemented. He had also pledged to cut congestion on all roads by more than 5% by 2010, as compared with a forecast growth of 15%.

The government's admission that it will not meet these targets is partly due to a bungle by government statisticians.

It has emerged that the statisticians set the baseline for traffic congestion in 2000 too low. The fact that congestion was already higher in 2000 than the government thought means it will be more difficult to bring congestion down.

However, the inability to meet the target also stems from the plan being far too optimistic about the number of councils willing to introducing congestion charging schemes. It was assumed eight councils would introduce congestion charging and 12 others would introduce parking levies. It is now expected there will be no more than three schemes to charge road users and one workplace charging scheme.

The Department of Transport estimates that urban charging schemes, such as the one to be introduced in London in February, will reduce congestion by 7%, while the Commission on Integrated Transport predicts they can produce a cut of 20 to 25%.

The latest failure over targets follows those on NHS waiting lists as well as on the government's drugs strategy. The Home Office has also abandoned plans to ensure 30,000 failed asylum seekers are removed from the country.