As the arrival of driverless cars gets closer, cities are scrambling to get ready. And for good reason: The driverless car promises to reshape the urban landscape as we know it.

Little wonder, then, that the potential changes are creating excitement—and fear—among city planners. As they host test fleets of robot vehicles and figure out how to rework ordinances to prepare for the autonomous future, they’re imagining what life is going to be like when the streets are filled with cars that can largely think for themselves.

Some see an opportunity to create on-demand public transit that gets people where they’re going faster and reaches more of the population. Or open up streets for more green space and greater walkability. Or redirect traffic to make it easier to hold functions like farmers markets.

But, even as they acknowledge the promise, others see possible problems. They warn that robot cars could encourage greater urban sprawl and cut into funding for public transit, widening the divide between the haves and have-nots. And driverless cars won’t be replacing all human-driven cars overnight, meaning an awkward mix of robots and humans sharing roadways.

Whatever the future holds, it will very likely be arriving soon.