On the other hand, redundant steering and braking seem like probable overengineering. Brakes are already somewhat redudnant (dual section master cylinders were common in the 70s and are almost certainly in any modern vehicle), and better software could periodically verify they're working and if not, coast to a stop. Steering failure could be handled by engaging the brakes. Simultaneous failure is likely rare and catastrophic anyway -- losing a wheel and having the brakes pressure go with it can happen, and when it does, you put on your blinkers and hope you come to rest in a safe manner.