Studies show that the majority of casualties on the road happen because of drivers not using proper following distances. It is not (yet) enforceable by cameras like speeding.

My idea is fairly simple and doesn't require new equipment: make a car's tail lights flicker to signal the driver behind that they're driving too close. Modern cars are already equipped with proximity sensors, so a simple software update would be enough to implement. The following distance is simple math based on the current speed. The blinking pattern could change depending on proximity.

Beyond simplicity, it would raise safety by appealing to drivers' personal responsibility instead of enforcing it.