CityMetric pointed in a recent article on Elon Musk’s vision for autonomous driving towards an interesting point regarding spacial limits: Musk’s vision that everybody will not be moving anymore with public transport but with autonomous cars that offer point-to-point travel is somewhat flawed. The limits are or geometrical nature due to the limit in capacity on the roads, crossings, parking etc. in urban areas.
While this limit is obviously correct for dense areas, there is also a simple market mechanism that can resolve it: that of road pricing.
Congestion based road pricing would allow the urban area to dynamically price the user on the actual demand/capacity and with this ensure a fluent traffic flow as well as, most likely, an affordable mass transit within urban dense areas. This would mean, that public transport will not face a fully dim future, but will rather focus on mass transit than to cover the last mile in peri-urban or suburban areas.