Downtown Brooklyn’s infrastructure will be overwhelmed by more than 40 million square feet of development in the next 15 years, according to a new study by a transportation think tank, Community Consulting Services. The city and the state will need to spend as much as $4 billion to handle the “traffic damages” resulting from the borough’s projected 24,000 new residents and 74,000 new jobs, the report says.

The think tank, which has produced several reports warning of the danger of overdevelopment in Brooklyn, looked at real estate projects that are under construction or planned; developments that will take place in the rezoned area of Downtown, and the developer Bruce Ratner’s Atlantic Yards project. The report defines traffic damages as congestion, traffic accidents, air pollution, traffic noise, vibration damage, pavement damage, and damage to private vehicles.

The report does not take into consideration the nearly 200-block Williamsburg-Greenpoint rezoning, which was approved yesterday by the City Council.

By 2008 alone, 31 projects are planned for Downtown Brooklyn, totaling 12 million square feet. That includes the expansion of the New York Marriott Brooklyn and the Atlantic Center, the executive director of the think tank, Brian Ketcham, wrote. In the downtown vicinity, another nine projects, such as the Ikea store and Fairway supermarket in Red Hook, and the Lowe’s store in Gowanus, will create nearly 6 million square feet of additional development in the next few years.

Those 18 million square feet of impending development downtown will create 26,600 jobs and attract 8,815 new residents, the report estimates. Each weekday, an additional 59,000 cars and trucks will enter the neighborhood, creating the need for 12,404 more off-street parking spaces. There will also be 189,000 additional subway riders and 47,000 additional bus riders.

The traffic damages will cost the city and state nearly $100 million a year, the report predicted.

Last June, the city approved a rezoning of 14.7 million square feet in downtown Brooklyn for office development, housing, and park space. The report by Community Consulting Services estimated the rezoning, which also called for the expansion of schools, would create 33,000 more jobs and attract 7,151 new residents. Twelve million additional vehicle trips a year would flood the neighborhood, creating the need for 3,700 more parking spaces. The cost of that congestion is estimated to be $83.7 million.

The Forest City Ratner plan for a Nets basketball arena and 8 million square feet of residential, commercial, and retail development at the Atlantic Yards faces heavy community opposition. If it receives the necessary approval from the city and state, however, it would bring 14,000 jobs and 7,920 residents to the area beginning in 2007. It will also generate 8 million additional vehicle trips a year to the area, and 3,000 more parking spaces will be needed.

The economic toll of the additional cars and density would be roughly $76 million a year, the report said.

“I think we are headed for a disaster,” the council member who represents downtown Brooklyn, Letitia James, said of the 41 million square feet of current and planned developments.

The total cost of the additional traffic will be $258 million a year, for a projected total of $3.9 billion by 2020, according to the report. The 115,500 additional cars, 430,000 subway trips, and 104,000 bus trips will translate into an estimated four fatalities a year, 476 personal injuries, and 930 additional property-damage accidents.

“Downtown Brooklyn will be a parking lot with increased pollution levels and major displacements of longtime residents – especially in the communities of color,” Ms. James said. She acknowledged that thousands of jobs will be generated by the growth, but she said: “It is important to look at who will get these jobs because there are no assurances that they will go to local residents, or that they won’t just be transferred from elsewhere in the city.”

A senior fellow at the Manhattan Institute, Julia Vitullo Martin, commented: “The report’s figures seem accurate, but the conclusion is wrong. All these projects are a good thing, the city is growing. It makes sense that it happen in Brooklyn, where there is a spine of infrastructure.”

Ms. Vitullo Martin, who has written widely on city economic development, said it is important that along with all the development in the borough, “we start thinking about the need for public investment in Brooklyn’s infrastructure.”