In this day and age, we have the technology to have sensors that measure distance and speed such as motion detectors, speedometers, speed cameras, alarms etc. We are more then capable of putting sensors on the front and back of cars for accident prevention purposes.
The idea goes like this. There is a sensor above every wheel of the car that can measure the distance between it and the nearest object. All this goes to a calculator type electronic chip. It can also measure how fast that object is going by deducting the speed between from the the speed of itself. Then it connected to the gears/brakes. It is programmed to calculate the likelihood of a collision and slow or stop the car accordingly. You could have a highway mode (long distance gaps between cars because of the high speeds), or parking mode (things can be a short way away, but the speed has to be slow).
The purpose of this is to prevent car accidents, one of the most fatal and crippling health problems of modern life. It could prevent or reduce everything from car park dings to pedestrian hits to highway pile ups. This will save fortune in hospital costs (for victims and governments alike), and in insurance payouts. The cost of putting the sensors in would be well and truly saved in mop up operation costs. It would also make life a whole lot more pleasant.
Because we can put sensors in cars as a safety mechanism, and car accidents are so horrific, I think putting them into vehicles should be compulsory by law.