Idiots like to tailgate even though they know it is dangerous. It is dangerous because of human reaction time which accumulates in a serious braking condition.
When the first driver brakes the one behind sees his lights and also brakes, third driver sees his lights and brakes too and so on. But
for every car there is an increase in reaction time being the accumulation of all the delays in front of him. Car number four or five gets squished.
My idea is to fit cars with a short range radio beacon at the rear and connected to the brake circuit and a receiver at the front connected to the brakes and the cruise control.
So, driver 'A' is cruising down the highway when driver 'B' snuggles in behind, as they tend to do. The receiver in B's car detectes the beacon in front and the cruise control adjusts speed to maintain a safe distance. The cars continue on until driver 'C' (and D,E,F and so on) joins them.
If driver 'A' brakes this signal is propogated down the queue and every car brakes at the same time!
I know there are following distance systems already baked and on the road but I have not yet heard of anything on the back of the vehicle.
A few refinements:
Spread spectrum technology would be used to avoid interference between different ensembles.
Putting on the indicators, to change lane or overtake etc, sends a 'disconnect' signal to be car behind you.
If a following car loses 'lock' it goes automatically slows, just like a cruise control does when disengaging a cruise control.
If there were two beacons, one at each rear corner, synchornised in phase the following vehicle could easily detect the exact centreline of the car ahead and use the error signal for input to the steering system, in this mode only the driver at that front of the squadron would need to actually drive!