A workplace parking tax would initially persuade just 5% of drivers out of their cars, an authority has admitted.
The figure has been revealed at the start of a five-day public inquiry into the proposed fee aimed at tackling congestion in Nottingham.
More than 100 employers, residents and experts have been invited to debate the charge, which could be as much as £350.
The city council said it had a duty to tackle the problem which is estimated to cost the economy £160m a year.
After hearing evidence from all sides, the independent chairman Brian Dodd suggested the council would use the tax purely to fund public transport like the tram rather than as a deterrent against car usage.
The council replied that what really mattered was improving public transport first with view to changing driver behaviour in the long term
The proposed levy would apply to businesses with 10 or more spaces and the initial annual charge would be £185 per space from the year 2010, rising to £350 by 2014.
Major Nottingham firms such as Boots, Games Workshop and Speedo will attend the hearing.
The council has said money raised from the tax would help make £12m to develop Nottingham's tram system.