My idea is simple, yet revolutionary. It comes in three steps.
1) Add a laser distance meter to the front bumper of every car, which is continually taking measurements of how car away the thing in front of you is.
2) Combine it with a computer that calculates the speed at which you are approaching the thing in front of you to work out a safe following distance for your current speed.
3) Hook that up to a set of speakers in the car that would play an annoying sound, which gradually increases in volume as you exceed the safe following distance (ie, as you get too close to the car in front of you.) My original plan was to put in a governor on the accelerator linked to the computer which would automatically cut out the gas as you got too close, but this seems like a better way of doing it.
Since I'm aware this wouldn't be the most popular invention...ironically, it'd be least popular among the people who need it most...I'm tempted to add 4) Design the whole thing so that it gives you a mild-but-painful electrical shock if you try to tamper with it.
Now granted, this isn't a multi-million dollar invention, because I'm pretty sure that nobody thinks of it as a quality-of-life improvement for their driving experience to have loud, annoying noises playing in their cars. But I'm also pretty sure that nobody enjoys having someone less than two feet from their rear bumper when driving at highway speeds, either, so it's just possible that we could get the government to mandate something like this in the same way they require seat belts and airbags. In a way, it makes even more sense; we're willing to spend millions to make cars more survivable in the event of a crash, so why wouldn't we spend about $150 to try to prevent the single most preventable accident there is?
I know, there's probably some crazy reason why it would be a bad idea. But given the amount of absolutely terrible driving I've seen in the last two days, just let me have my dream, okay?