If networked, they can and will be hacked.
How unpleasant to know your destination has been changed in route to Grandma's. Little Red Riding Hood would not approve, but who gives a damn what she thinks.
Incidentally, you KNOW they will be networked to avoid collisions on the freeways, roads, and back alleys of America and to let big brother know your every move, real-time and historically. Don't believe me, then ask them to show you the pictures.
And when the server goes down...you're stopped dead in the water (not literally I hope) and miles away from nowhere or worse. If you have a manual override and a permit to drive you may continue, otherwise you may be SOL. Be sure to pack a lunch and bring your overcoat just in case.
And be sure your software level is updated to the correct level. Always file a "flight" plan with the government authorities in case you don't arrive and they have to start a search.
Never tamper with or attempt to override the speed throttle controller. Big brother will take care of all adjustments needed to assure you (and thousands of other concurrent users) will arrive in a safe and timely manner. Pray there are no "blue screens of death" while enroute to your destination.
Yep, it's a carefully thoughtout plan. Would big brother lie about this? Hackers are going to have a field day and there's going to be blood on the highways.
Unless networked, much of the potential safety and efficiency benefits will be lost.
But it’s not impossible to imagine a hacker taking control of the system and deciding to play continent-wide bumper cars.
Forbes Demonstrates “Car Hacking” the Michael Hastings Murder Method
https://www.youtube.com/watch?v=1CpPAjVh3dM
Michael Hastings Car Hacked and Remotely Driven into a Tree to Murder Him?
https://www.youtube.com/watch?v=qQrHnP9lXIU
Car Hacking - Remote Control Murder of Michael Hastings
https://www.youtube.com/watch?v=BiD-x07iUGU
How Hackable Is Your Car? Consult This Handy Chart
http://www.wired.com/2014/08/car-hacking-chart/
The 20 most hackable CARS revealed: Report lists the smart vehicles that are most at risk of having their systems hijacked
http://www.dailymail.co.uk/sciencetech/article-2719866/The-20-hackable-CARS-revealed-Report-lists-smart-vehicles-risk-having-systems-hijacked.html