The number of cars daily coming into the original charging zone and into the western extension has dipped, Transport for London (TfL) statistics revealed.
But roadworks and traffic management schemes have greatly reduced the road capacity in both zones.
This has resulted in congestion returning to levels experienced before the charge was brought in.
London Mayor Boris Johnson said he had asked TfL to hurry up with his plans to improve traffic flow, including allowing motorbikes to ride in bus lanes, rephasing traffic signals and cracking down on delay-causing roadworks by utilities.
A TfL spokesman said: "Without the congestion charge, the traffic problems in London would be much worse."
The congestion charge generated provisional net revenues of £137m in 2007/08.
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Mark, South Manchester (07/08/2008 at 09:32)
That's what the congestion charge is all about folks. A backdoor tax revenue making scheme for local councils - and nothing to do with congestion at all!!