The autonomous car isn't going to make traffic, construction, nor other idiot drivers magically disappear, so I'd say this is a hopeful but doubtful claim.
Automation will open up car travel to populations (the young, the elderly, the visually or otherwise impaired) who did not previously have access. Self-driving cars could increase the overall amount of vehicle miles traveled.
Except that these are the people that almost always have someone ELSE drive them places (loved, ones, friends, taxis...), requiring pickups. So it's easy to argue that they could decrease the overall amount of miles travelled very easily. Nevermind the automated vehicles would presumably use smart navigation to avoid traffic, take the shortest routes possible, and drive under the speed limit.