So imagine it’s the wonderful future, and everyone has the option of being ferried everywhere by autonomous cars.
The places that were once parking lots have been converted into parks, shops, or homes; the places that were once useless archipelagos of land trapped within highway cloverleafs have been converted into vertical parking lots for autonomous cars, which are capable of holding far more cars within a given space than any traditional parking lot ever could.
Getting Around
Upon entering a car at the front door of one’s home, and perhaps after deciding whether or not to drive the car or let the car drive itself instead, passengers will be confronted with a choice of three basic transportation options:
The most expensive, but also simplest and most private, option is to travel directly by car to one’s destination.
The second most expensive, but generally fastest, option will be to travel by car to a train station, then travel by train to another train station and, if necessary, travel by another car from the station to a destination. In this future, the middle lanes of many urban highways will be converted into surface rail lines, making trains more widely available. (Also, subway systems will likely continue to expand over time). After dropping off passengers at these highway train stations, cars will be able to drive on to the nearby vertical parking lots.
Finally, the cheapest but slowest option will be to travel by car to a cable-car station. Cable-car stations will often be located within highway vertical parking lots, and also directly above highway train stations. After travelling by car to the nearest one, passengers will ride a cable-car to the train station.
In some places, cable-cars will also diverge from the highway, in order to link the highway to nearby areas that would otherwise be hard to reach as a result of barriers like rivers, escarpments, or valleys.
These cable-cars will not be eyesores — as are some current urban cable-cars, such as London’s Thames River cable-car; and as a monorail would be — as they will travel low to the ground in the middle of wide highways, rising higher only on occasion, mainly to pass over bridges that cross over highways.
Cable-cars will be the third option, for those not in a rush who are looking for a cheap way to travel. Their main purpose will be to link highway parking lots with highway train stations. This will be useful given that highway train stations will be spaced quite far apart from one another (since building train platforms in the middle of wide highways will be relatively expensive), and given that many parking lots will be located within the otherwise difficult-to-reach archipelagos of highway cloverleaf intersections.
As a bonus, cable-cars will increase the overall transportation capacity of a highway by roughly 2-4 thousand people per direction per hour, as well as overcome any topographic barriers adjacent to the highway. They will be particularly useful for highways that run along the floors of valleys, as many urban highways do.
What About Without Autonomous Cars?
This future arrangement does not even necessarily require fully autonomous cars. Semi-autonomous cars would be sufficient:
So long as cars could function autonomously from, say, 4am-5am, and so long as cars could function autonomously within vertical parking lots (which, unlike traditional parking lots, would be able to fill almost every last cubic metre of their volume with cars), the system could work. Passengers could order a car, and it would be delivered directly to their home overnight.
Future Economics 