New Yorkers will be able to walk, bike, and jog across a seven-mile stretch of Manhattan free of cars for three Saturdays this month as part of Summer Streets, an event organized by the city government to encourage alternative transportation.

On August 9, 16, and 23, between 7 a.m. and 1 p.m., the car-free route will begin at the Brooklyn Bridge and run along Lafayette Street, Fourth Avenue, and Park Avenue up to East 72nd Street. Rest stops along the way will provide water, and organized activities including dance classes, bike rentals, and children’s games will be offered along the route, along with live music performances.

Mayor Bloomberg talked up the first of the three Summer Streets events at a press conference yesterday in Lower Manhattan with the hip-hop mogul Jay-Z, whose real name is Shawn Carter, and the transportation commissioner, Janette Sadik-Khan.

Calling Summer Streets a “grand experiment,” Mr. Bloomberg suggested that the city could organize such an event again in the future and possibly expand car-free days to other areas if this event proves successful.

Mr. Carter said learning to ride a bicycle at age 4 was one of his “proudest moments” and that he still bikes regularly. “I ride all throughout the city,” he said.

Some business owners along the route have complained that Summer Streets will disrupt their sales, and taxi drivers have warned that it will slow their driving. Mr. Bloomberg said he expected business to benefit overall from the pedestrian-friendly streets.

“It probably will be pretty good for business,” he said. “It should bring out, if the weather is good for those three Saturday mornings, a lot of people who would not normally come.”