Excellent question. It takes decades for new features to fan out to the majority of new cars. After that it then takes decades more for those features to reach saturation of all cars on the road, because only 7% of the car population turns over each year.

The bottom line is it's generally 40 years from the point when features like seat belts, air bags, traction control, and backup cameras are first introduced and when they reach 95% saturation.

Throughout this adoption process, demand for these features among those whose cars don't have them increases significantly!