Braking the tailgate habit

What happens when you're driving on the freeway and the brakelights of the car in front of you come on?

You slow down, so you won't hit the car.

What if the car had sensors in the back (similar to the sensors that signal when you're backing up and about to hit something) while you were driving that, based on your speed, looked for nearby objects.  If something came near (like a tailgating car), your brakelights would light up (even if you are not actually braking) -- signaling that tailgater to slow down and avoid a collision.

This idea could save lives, and potentially teach drivers how close is too close.