I think Autonomous technology will allow for more cars to exist on the road because they will be able to communicate with one another thereby allowing them to travel closer together.
For instance: if 20 cars are closely tailing one another 1 foot apart and the 1st car has to slow down....the information from the first car will get to the 20th car behind it in a matter of milliseconds and they will all slow down simultaneously. There will be no need to for fully autonomous cars to have to just be concerned with what the car in front of you is doing as AP does today.
Cars will be able to travel a foot apart in a 200 car line and each car will know exactly what the first car is doing almost instantly. As a matter of fact when you press a key down on a computer...the computer has completed the function you requested and has been sitting there waiting for 100,000,000,000 cycles before the key comes back up.
I watch the packets of Bluetooth and WIFI (using Wireshark) and noticed that my computer is doing NOTHING 99% of the time. Thats the speed that automobiles can now communicate miles apart. I can't wait to see a 3 mile train of cars moving at 90mph all braking at the same time. Its going to be amazing.