More than 356,000 people walk through the heart of New York City each day, but imagine how many more could traipse through if Times Square was closed to cars?

Advocates of a radical new plan want to close 42nd Street to car traffic and create a light rail system to run across the island of Manhattan, from the Hudson River on the west to the East River on the east. Such redevelopment would boost the local economy and improve transportation, according to Vision 42, a citizens’ group formed in 1999 by the Institute for Rational Urban Mobility. It would also offer a less polluting travel option than the exhaust-belching buses that currently take New Yorkers across town at a snail’s pace, The New York Times reported.

At a cost of $500 million, the light rail would stop at every avenue and run from one side of the city to the other in about 20 minutes, about half the time it currently takes to ride a bus across town.

So far, property owners along 42nd Street support the proposal — but the city isn’t so sure. But even though city officials aren’t rushing to embrace Vision 42’s idea, they have launched “Green Light for Midtown,” a project to alleviate congestion in Times Square, where traffic moves an average of 4.2 miles per hour. The city has created several pedestrian malls in midtown, and over Memorial Day weekend officials closed several blocks around Times Square to cars.

But proponents of Vision 42’s plan say the city needs a permanent solution.

Vision 42 advocates pointed out that light rail lines have stimulated economic growth and development in other cities, such as Dallas, Portland, Ore., and Phoenix. According to a study by the consulting firm Urbanomics of New York, closing 42nd Street to cars and adding a light rail line would boost the economy in Manhattan: Pedestrian volume would increase by 35, translating to some $380 million more in sales among the street’s 126 stores.

Indeed, proposals to expedite cross-town traffic in Manhattan have been kicked around for years. An older proposal, which lost steam in the 1990s, would have created a trolley line along the south side of 42nd Street, with the north side open to vehicular traffic. But New York City Mayor Michael Bloomberg favors extending an existing subway line – the No. 7 – to reach farther west.

“The real gain here is you could handle three times as many people with roughly the same cost,” said George Haikalis, an engineer and a co-chairman of Vision 42. “A lot of people have expressed interest in this, but have not signed on, because they’re awaiting interest from Mayor Bloomberg.”