On highways, when a car is on cruise control, the car should stay in lane automatically.
We are not aware of any car maker offering this today, but it may be available soon. The largest impediment is the legal status if something goes wrong. The cost is likely more than a lane departure system, but with electric steering, perhaps not much more. The retail cost is likely in the $1000 range for such a system.
Implemented in Tesla cars built after November 2014.