However, during off-peak periods, journey times had increased by one minute over the 3.5-mile-long stretch of motorway.
The £1.9 million scheme on the M4 to the west of London was launched by Mr Prescott in June 1999,
It has now been given the government's seal of approval after a case study showed it had cut rush-hour journey times for both cars and buses.
Only buses, coaches and taxis can use the lane which runs on a section of the motorway between Heathrow airport and central London.
It attracted publicity shortly after it was opened, when it was claimed that a car taking Tony Blair back to London had "cheated" and used the bus lane after the prime minister got stuck in a jam.
The long and the short of it
A report, published on Tuesday by the Highways Agency showed that on average, each bus was saving 3.5 minutes and each car one minute, in journey times during peak periods.
However, during off-peak periods, journey times had increased by one minute over the 3.5-mile-long stretch of motorway.
The study, carried out by the Transport Research Laboratory revealed that although there had been an increase of nearly 2% in the total time spent travelling on the section of motorway affected by the scheme, journey times for all vehicles had become more reliable.
It concluded that there was no evidence that surrounding roads had become busier due to drivers diverting off the M4 to avoid the lane.
However, the AA remains sceptical by the findings, saying the bus lane could only be hailed a success if "significant numbers of drivers switched from their cars to public transport".
Under the scheme, speed limits on the two remaining lanes of the motorway were reduced from 70mph to 50mph.