I feel like we have the technology to prevent a car from starting if the driver is significantly impared, but "solving" addiction, cancer, and heart disease are much harder problems.

Obviously it would need to be implemented carefully, but I personally would be more than fine blowing into a tube to start my car if it meant saving 12k lives a year with a very low false positive rate.

That being said I know it would never be implemented in a sane way in the US, and you would probably have situations like your car insurance automatically increasing due to a faulty sensor, so I'm ultimately against it unless a lot of other stuff changes.

But it's still much more possible than "preventing drug addiction"

That's already a huge number. But it's ignoring the much larger issue of distracted drivers, usually on their phone.