Kingston, Richmond and Wandsworth councils decided to prepare traffic figures to show the effect of each of the draft proposals by the Royal Parks Agency.
Kingston Liberal Democrat Councillor Derrick Chester said: "I look forward to the Three Boroughs Group entering into a constructive relationship with the Royal Parks Agency to protect and improve the environment of the park, the surrounding road network, residential areas and green open spaces."
He said it was a constructive meeting which would enable any figures produced by the parks agency to be scrutinised for accuracy.
Wandsworth Councillor Tom Harris was elected as chairman of the forum, which will have its first public
meeting on June 30.
The agency is also consulting the public during the summer, via exhibitions.
The draft proposals drawn up by the agency were rejected by Kingston Council's traffic experts earlier this year.
The agency agreed to examine fully the effects of their proposals.
The plans include peak hour closure of roads at Pembroke Lodge, Sheen Gate and Robin Hood car park, plus permanent closure of Ham Gate to cars.
There is also the possibility of reducing the speed limit to 20 mph and shutting Pen Ponds car park.
Environmentalists say that severe measures are needed to curb the daily destruction of the park.
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