> Cruise control, now, that really is useful because it automates a trivial chore (maintaining a steady speed) and will do it well enough to improve your gas mileage. The main failure condition is "car keeps driving at full speed towards an obstacle" but an automatic emergency brake feature (again, reasonably straightforward, and standard in many new cars) can mitigate that pretty well.

Adaptive cruise control also helps; if the system detects a car in front slowing, it'll slow at a roughly equivalent pace to avoid a collision.