That's all fine, but we also have decades of experience designing systems for exactly this - they are called train drivers. Driving a train can be the most boring job in the universe, in ways that driving a truck isn't - there is very little feedback from the controls, you can be going for hours in a straight line without any need for input or change of speed - so locomotive controls are designed to require constant positive input to keep the driver engaged. This should be the same - the system should require the backup driver to keep confirming/selecting something on the dash, even if it's inconsequential to the operation of the system.
