Because an automated system would be less prone to congestion, and the average time for travel would go way down. You'd have to do the math to find the break-even point, but I'd imagine that you could add many more cars into an optimally flowing traffic system and still end up with less total running time.
Like I said, you'd have to do the math. It's very possible that's true. But it's not a certainty. People have a limit on how much they want to drive regardless of how easy it is. After all, the store itself will still suck when everyone decides to go at 5.
I'm in NYC, I could hop on the subway any time I want without any hassle at all, but it's not like I do just because the option's there. Transportation is a means much more than an end for most people.
Uh, maybe you'd have to look at the history of urban planning for the past 50 years? In densely populated urban areas, just about every time people add more roads, the capacity gets used up by increased development in the outlying areas served by those roads.
Network bandwidth and CPU capacity are subject to the same phenomenon. Do end-user desktops really have more functionality than 10 years ago? Besides things like increased 3D graphics capability and more things to do with a web browser and an internet connection, not so much. As bandwidth has increased, the amount of data in a webpage has increased, and it becomes practical to use a web browser for more.
Basically, there can be a certain amount of pent-up "latent demand" which is there but which can't manifest until the roads are built and such travel becomes practical.
I'm granting that miles driven or number of cars on the road could go up, maybe way up. I'm just guessing, subject to actually doing the math, that increased efficiency and assumptions of reasonable limits on how much latent demand is actually out there could be sufficient to make time spent in cars, fuel consumption, emissions, or other metrics better regardless. Since we're using networking analogies, basically I'm guessing that current uncoordinated human-driven traffic is copper wire to an automated system's fiber-optic cable.
But again, it's just a guess, and I'd be the first to accept that I was wrong if the numbers didn't actually work out.
