[eschaton]

Honestly, thinking about how cities will be retrofitted to deal with autonomous cars isn't too difficult, because it mostly means cities becoming similar to what they were like in 1900. Yes, there will be autonomous car traffic on the roads, but there will be little danger to pedestrians, and little reason for parking. Just start demolishing garages (both residential and commercial), narrowing roads, and filling in parking craters and you'll get most of the way there. Hell, once conversion towards automated systems is universal, you could begin seeing an argument towards eliminating highways, as AI should be able to drive on surface streets at near highway speeds (effective, not constant) without putting pedestrians in danger.

A deeper, and more difficult question, is what suburbs will start looking like, since they were built from the ground up with cars in mind, and there's going to be a lot less cars in the future.

Clearly garages (particularly modern 2-3 garage monstrosities) won't be needed for the most part. Some suburbanites might desire ownership of a car, and keep it in their garage, but others won't have any. Garages will have to be retrofitted to new uses - likely junk storage - and new construction in the suburbs will potentially have very different typologies than today.

Beyond this, I'm guessing "legacy" suburbs will remain largely the same as they are today. There's things you would likely not do in an autonomous car world, like 15-foot setbacks and cul-de-sacs, but we are stuck with them without heavy re-engineering. And I don't expect that self-driving cars will actually make people walk much more than today, so the trend towards walkable communities won't pick up dramatically. Cities may become places the car is (mostly) banished from, but suburbs won't change much besides home design.