Get ready for even more cars on Boston streets

The wave of big buildings transforming much of Boston is bringing a lot of new housing and jobs. And a whole lot more cars.

Despite building near transit stations and carving room for Zipcars and Hubway bicycle stations, developers expect that many residents in their new projects will still have cars. Taken together, that will add thousands of new cars to the old cowpaths and post roads that snake through the city.

Case in point: The companies behind the massive redevelopment of the old Edison power plant in South Boston estimate the proposed complex of housing and office space will add nearly 9,000 car trips a day.

Making room for them in South Boston’s already-crowded streets, and in other neighborhoods with similar large projects, won’t be easy, said former state transportation secretary Fred Salvucci.

“I don’t think there’s any place in the city that can afford more automobiles than it has now,” he said. “We are right near the point of getting too full.”

Despite being one of the most densely packed, transit-friendly cities in the United States, Boston still leans heavily on cars. Hundreds of thousands of commuters drive to work in and around Boston every day. And within the city, 45 percent of working residents — 151,000 people — commute by car, according to the Boston Planning & Development Agency. About half of South Boston residents drive, an even higher share in Charlestown and Dorchester.

And most drive alone.

Other big projects that will generate even more traffic include the expansion of the South Bay shopping center — some 6,250 car trips per day, according to estimates from the developers, who are planning 475 apartments, new retail, and a movie theater along a busy stretch of Massachusetts Avenue.

The South Bay developer, Edens, has contributed to road improvements, including extending a street onto the property to make access easier, and new traffic signals at key intersections around the site.

“The ability to have a developer upgrade that stuff helps us a lot,” said Tad Read, a senior planner at the BPDA. “It was a great example of leveraging the resources associated with a big project.”

Still, some projects are so big they make neighbors nervous. Diane Valle is among a group of residents advocating for a smaller version of One Charlestown, the proposed remake of the Bunker Hill public housing complex that would triple the number of units there. Adding more than 2,000 apartments and condos to the hard-to-reach back side of Bunker Hill could further clog the narrow streets of Charlestown, she worries.

“It already takes forever just to drive to the post office,” Valle said. “We’re on an island here with three roads in and three roads out. How much can we absorb?”

It’s worth noting that some of the new traffic is just old traffic relocated, said Eric Bourassa, transportation director for the Metropolitan Area Planning Council. Someone who lives in the South End might move to a new building in Charlestown, adding a car to one neighborhood, but subtracting from another. Studies don’t typically measure that.

Still, Bourassa said, on balance the new growth will put “more constraint on our transportation system.”

And it’s already straining. Nearly 40 percent of major roadways in Boston and eight neighboring cities are congested during the afternoon commute, according to a 2016 study by the Boston Region Metropolitan Planning Organization, which directs federal transportation funding in Boston. By 2040, the number of congested roads will increase to 51 percent, with large-scale developments directly contributing to that increase.

Those big projects have ripple effects as motorists learn to avoid those areas, increasing traffic on newly beaten paths across the city, the study argued.

Boston’s population has grown by more than 100,000 since 1980, with another 55,000 projected by 2030.

Vineet Gupta, planning director for the Boston Transportation Department, said the city is preparing for the influx of cars from new residents, pointing to a transportation plan issued in March that laid out strategies to absorb the new traffic.

Part of the solution, city officials said, is to give residents more ways to get around. Hubway stations and car-share parking are now standard at many larger apartment buildings. Shuttle buses — long part of the menu in job-thick neighborhoods such as the Seaport and Longwood Medical Area — are becoming a residential amenity too. Just last week the BPDA approved a 12-unit apartment building in Mattapan that will run a shuttle to the Forest Hills MBTA station.

“We’re not saying people aren’t going to drive cars,” said Jon Greeley, head of development review at the BPDA. “What we are saying is we want to give people as many different options as possible.”