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Photographer: Brent Lewin/Bloomberg Photographer: Brent Lewin/Bloomberg

Have you imagined a future in which super-smart robo-taxis make urban gridlock a thing of the past? Keep dreaming.

As autonomous vehicles and mobility-on-demand services continue to grow over the next decade, travel time and traffic jams will increase rather than decrease in downtown areas, according to a new study from the World Economic Forum, the Boston Consulting Group and the city of Boston.

Overall, average travel time in Boston will decrease by 4 percent, and eventually only half as many parking spaces in the city will be needed, according to the study. In neighborhoods outside the core of the city, autonomous ride-sharing services will mostly replace the use of personal cars, and travel time will decrease by 12 percent. But in downtown areas, autonomous vehicles will most likely be a substitute for short public transportation trips, increasing travel time by 5.5 percent.

“I think cities have moved away from the thinking that autonomous vehicles are going to be some kind of heaven and realized increasingly that street space is not an infinite, boundless good,” John Moavenzadeh, an author of the study, said by phone. “Moving forward, cities are going to be thinking more strategically about this asset and realize they need to be at the table with the companies investing in autonomous technology.”

His findings echo others’ cautions. A 2017 study out of the University of California, Davis concluded that ride-hailing services would likely increase street traffic in major cities, and Toyota Motor Corp. expressed concerns in 2014 that autonomous cars would contribute to urban sprawl and pollution. As autonomous technology begins to reach cities and app-based ride-hailing services continue to grow in popularity, the Boston study encourages city governments to take measures to solve the impending downtown traffic problems, such as financial incentives to discourage single-occupancy rides.

Read more: Carpools are a must to avoid congested self-driving dystopia

Moavenzadeh said that while consumers may be interested in shifting away from public transit toward autonomous vehicles and rides on demand, stronger public transportation systems will be vital to solving the traffic problem in downtown areas.

“It’s not about convenience, it’s about competitiveness and the employment market,” Moavenzadeh said. “If young workers see a clogged city and a moving city, they’ll choose the moving city, and both public transportation and autonomous technology will be a part of winning that mobility race.”