When the drivers behavior is deemed to have deviated from the norm by more than a certain amount, such as if a driver is ill, tired or injured, the car's control systems automatically adjust the vehicle responses to compensate. This vehicle would use some of the types of technology used in the autonomous vehicles seen in the DARPA Urban Challenge. The experimental vehicle was devised to help older drivers but the same technology could be used to improve safety for younger inexperienced drivers and also to improve fuel efficiency. A vehicle could be automatically programmed to perform some of the techniques already employed by hypermilers to get the most out of a hybrid system. Unfortunately, the technology is still at least two decades away from real applications. Programming a system to monitor the widely varying behavior of a human to learn patterns and then be able to adjust a vehicle's behavior is an incredibly complex task.
[Source: Boston Globe, thanks to Rick for the tip!]