Urban planners are pushing to transform 42nd Street into a pedestrian mall, complete with its own street-level rail line.

The transformation, which advocates say would turn the clogged streets into a narrower version of an Italian piazza, would boost business on the strip by up to $500 million a year while cutting crosstown travel time in half.

The main group promoting the idea, Vision42, released a study Tuesday supporting its claims. Retail and restaurant business would jump 35% to $1.49 billion a year with more pedestrians on the streets, according to the study.

That would increase tax revenue by an additional $28 million a year for the city and state.

Vision42 backers say the light rail, which would run river to river along 42nd Street, and pedestrian mall would boost property values by $3.5 billion which would translate into a $277 million boost in property taxes.

Still, the project is years away, if approved.

It would cost an estimated $360 to $510 million to convert the streets and build the light rail system. City Hall has yet to endorse the project.

"Most people are interested but cautious," said George Haikalis, co-chairman of Vision42 and president of the Institute for Rational Urban Mobility.

"This is a heavy lift and it would take the mayor's unabashed support for it to happen. So far, he has not signed on to it."

The city Department of Transportation remains cool to the idea. It is worried that businesses would be unable to receive deliveries if the street was closed to traffic. It also says the city's main Midtown focus is on the $2 billion extension of the No. 7 train west to 11th Avenue and south to 34th Street.

"We've met with the institute to discuss its proposal in the past and we'll review the economic studies they recently released but our focus is on the extension of the no. 7 train to increase mobility on 42nd street," DOT spokeswoman Kay Sarlin said.