This story from engadget.com tells us that Google has applied for a patent on gesture-based car controls. Their proposed system relies on both a ceiling-mounted depth camera and a laser scanner to trigger actions based on an occupant's hand positions and movements.
Examples they cite are: Swipe near the window and you'll roll it down; point to the radio and you'll turn the volume up.
Examples they don't cite are: Wave both arms in the air and you'll crash; give a one-finger salute to a Police vehicle that is following you and you'll get arrested.
Apparently, Google has acquired a motion control company so they will be looking for uses for it.
I'm not convinced this is the best one.
Voice-activated controls are improving so that they are actually usable now, combining them with this may actually make it more dangerous to be in a car - what if a nervous passenger finds a spider in the car?
Besides, Google are also developing their driverless cars so none of this should be needed.
As ever, I do enjoy reading the comments at the bottom of online articles - this one produced some good ones:
Examples I cite are NewGawker, who states "This won't work in Italy" and my personal favourite, fsmarin who, on seeing the picture above asks, "Why is a monkey driving a bus?"