The congestion charge has been so successful at persuading drivers to leave their cars at home, it took almost £1m less than predicted in its first week.
Traffic dropped by 25% last week
Traffic reports suggest the £5 daily charge is still keeping vehicle numbers down by 20% in central London, despite schools returning after half term.
Transport for London had predicted an average 750,000 of the £5 daily payments a week, or around 640,000 a week during the school holidays.
But the success of the scheme, which saw the number of vehicles in central London drop by 25% in its first week, meant just 460,000 payments were received.
Week One Facts
87,000 drivers paid for last Monday
92,000 drivers paid for last Tuesday
94,000 drivers paid for last Wednesday
15,000 people to receive penalty charge notices
Transport for London (Tfl) director Derek Turner said he was not worried by the news.
He said: "This scheme is not about producing revenue, it is about reducing traffic in central London and we have achieved that.
"The revenue is secondary to the scheme.
"We were actually adding additional items to our budget to be paid for by congestion charging, but there will just be fewer of those."
TfL predict the scheme will raise £130m in its first year to fund improvements to public transport in London.
Opponents of the scheme were waiting to see if it would struggle to cope after a smooth first week of operation with the return of the school run on Monday.
But traffic reports suggest vehicle numbers are up from last week but still 20% down on normal levels.
Mr Turner said: "We expect there to be some glitches and some teething problems as the system comes under increased stress.
"But we're quite hopeful, particularly as we believe the London travelling public is recognising it's a very successful system."
Conservative mayoral candidate Steven Norris promised to scrap the scheme if he is elected in 2004.
"Even if this works in the way Ken Livingstone thinks it will, it is fundamentally wrong. It's wrong for London as a centre of business, it's wrong for Londoners," he said.