A business survey suggests
most London companies still believe the congestion charge is a success and has enhanced the city's image.
Journey times have been cut by a third
The survey of 500 businesses "of all sizes and sectors" marks the six-month anniversary of the road toll.
Commissioned by London First, a business membership organisation which supports the charge, it found 49% of companies believe the scheme works, 35% are undecided and 16% think it is not working.
The daily £5 charge to drive into central London, was intended to cut congestion which the mayor said cost the city millions.
Some smaller businesses have been reporting a drop in profits since the charge was introduced.
Traffic levels have fallen by 20%, but the survey found 71% of firms are still waiting for the charge to have a noticeable impact on their profits.
The remaining businesses were evenly split between noticing a "very positive impact" and an adverse effect.
Only 2% said they would consider leaving central London and 34% felt London's image had been enhanced by the scheme.
Julia Lalla-Maharajh from London First, said: "The results demonstrate that support for congestion charging among the business community remains firm.
"What is clear, however, is that businesses feel they do not know enough about where the revenue is going, while one fifth felt that the technology was inadequate."
Last month, Transport for London (TfL) announced the charge had been 'too successful' with fewer motorists than expected willing to pay.
This resulted in a £64m budget shortfall, meaning some transport projects had to be shelved and the private company which administers the charge has been given £31m from the budget.
Paul Watters from the AA Motoring Trust said they were concerned that TfL was still spending millions on a study to expand the scheme further into Westminster, Kensington and Chelsea.
He added: "It's way too premature to consider expanding the zone, when the jury is still out on the overall success of the scheme in central London."