A new study — based on testing underway in Boston — predicts driverless cars could cut much of the traffic clogging the city’s streets, reduce air pollution, and free up space used for parking.

The report, from Boston Consulting Group and the World Economic Forum, which joined with Boston officials in 2016 to develop self-driving car strategies, is geared to global policy makers as they grapple with the ascending technology.

But it is based on local information, using models of present-day Boston traffic. The report predicts that vehicle traffic could decrease between 11 and 28 percent, and average travel time for commuters could fall from 11 to 30 percent.

Moreover, carbon dioxide emissions could drop by as much 66 percent, and Boston would no longer need many parking spaces because self-driving vehicles would continuously provide rides to people who no longer would have to drive in the city.

The optimistic predictions are based on the assumption the technology would be most widely used for taxis or shuttles, leading to a decrease in personal vehicle use. The report also assumes driverless cars will run on electricity rather than fossil fuels, benefitting the environment.

There are some drawbacks, however: If driverless technology becomes cheap and easy, more travel may result in more traffic. Empty cars cruising the streets while waiting for passengers could also be counterproductive. Commuters could move farther outside the city if traffic improves, leading to more sprawl. And, traffic aside, cabbies and other commercial drivers could be put out of work because of the technology, the report says.

Two Boston companies, ­nuTonomy Inc. and Optimus Ride, are testing self-driving vehicles in the Seaport District, where they are each headquartered. A third company, the global auto parts supplier Delphi, is also permitted to test in the neighborhood, but it is not clear if it has begun doing so.

Adam Vaccaro can be reached at adam.vaccaro@globe.com. Follow him on Twitter at @adamtvaccaro.