If somethings got to go, the obvious choice is cars. Indeed, that's what cities like London have aimed to do with initiatives like congestion pricing, which attach a prohibitively heavy cost to driving during the most congested times of day.

Rather, they attach an accurate price, forcing drivers to pay some of the costs that they generally impose on the public. I mean, the amount of space required per driver is wildly disproportionate with the demand on a public resource that every other form of transportation requires. Then there are the environmental costs, which include both noise and pollution. Again, these are way out of proportion in terms of the number of drivers vs. non drivers. They also do damage to commerce, in that pedestrian friendly zones are far more amenable to shopping, dining, etc. than streets that give preference to the needs of drivers. And of course, cars are basically lethal, whereas pedestrians, bikes, and even busses (especially when they have their own lanes) generally aren't.

Basically, cars are a bad deal for cities, and the 21st Century is going to see a sharp and concerted effort to push them out. Letting them in was a mistake. It's time to undo that error.