Over the coming decades, a dozen dense and developed cities may aggressively use shared fleets of electric and self-driving cars that could be summoned to pick up passengers and shuttle them to offices and stores.

Such cars, which could carry anywhere from two passengers to 20 passengers, could cost less to use and be more convenient than owning a car, according to a new report from the research firm Bloomberg New Energy Finance on Tuesday.

Cities with the greatest potential for such futuristic urban transportation include London, Shanghai, and Singapore. These cities generally have high incomes and GDP, dense populations, and a history of investing in new, public infrastructure.

New transportation options could effect how cities are planned, requiring fewer parking places and more zones for picking up passengers and dropping them off. It could also increase how much people travel—because of its lower cost and convenience—by up to 30% more miles.

Not all cities will develop such futuristic urban transportation. In contrast, the report predicts two other possible scenarios for how electric cars, autonomous vehicles, and ride sharing will affect cities.

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Cities in developing countries like Delhi and Mumbai will likely rely less on autonomy, and continue to rely on human drivers due to the low cost of labor and lack of investment in roads that self-driving cars would need. But these cities will look to car sharing and electric vehicles to help lower traffic congestion and reduce pollution.

Another scenario is that private cars will remain king for decades in cities with a lot of urban sprawl like some in Europe and in North American suburbs. Cars there may be self-driving and electric, but they won’t be as readily shared.

The combined impact of electric cars, car sharing, and autonomous vehicles will utterly change urban transportation, the report says, echoing the statements of GM’s CEO Mary Barra last week. Barra also added connectivity to the list of possible major changes to transportation and noted that sharing could potentially be more disruptive to GM than electric cars or autonomous vehicles. GM has invested in ride sharing company Lyft and recently bought autonomous vehicle tech company Cruise Automation.

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Other automakers and ride sharing companies have been focusing on these technology trends for a while. Uber has a fleet of self-driving cars in Pittsburgh while Tesla’s TSLA Elon Musk laid out his vision of shared autonomous electric vehicles earlier this summer.

The Bloomberg New Energy report found that the combined impact of these trends could be really powerful. For example, sharing cars could make electric cars more cost effective, because the cost of ownership is less when cars are used more intensively by multiple people.