Traffic levels in central London have dropped since the congestion charge zone was extended, the London Mayor Ken Livingstone has said.
Critics say the half term break distorts initial figures
The £8-a-day road toll scheme now takes in most of Westminster and Kensington and Chelsea in west London.
Traffic levels within the new zone have fallen by 13% since half term ended, while traffic volume in the central London zone has remained static.
But critics have said it is too early to measure traffic levels.
Mr Livingstone said: "These initial figures are highly satisfactory. In the early weeks following the extension, traffic is down in line with expectations.
"In the existing congestion charging zone the results are exceeding the traffic modelling with no increase in traffic."
But Angie Bray, of the London Assembly Conservatives, said it was too early to start praising the scheme.
"Half term ended in the middle of February so therefore his analysis is about two weeks worth.
"He is basing its performance on two weeks of congestion charge figures and that's just preponderous," she added.
"How can you possibly measure the impact of a major piece of new transport policy in that time. It beggars belief."