For instance, how many people ride in the car? What is the average car trip length? Why and when are people driving? Speed profiles, line of site in both car and environment. Does traffic all flow one way, can a car ever land in incoming traffic if it loses control, are traffic barriers designed to bring an out of control car safely to rest with good line of sight to the accident? Are features keeping drivers alert or distracting them?
The difference between lots of fender benders with a bit of panel beating and constant fatalities can come down to multiple causes, many outside of engineering a safe car.
There's no good reason not to, for example, have every car use a breathalyzer to start the engine -- those driving drunk on occasion would protect themselves from DUIs, lives would be saved, etc. Or to implement other, similar deep regulations. But the ideology around cars ("freedom"), vs. planes ("safety"), is too different to allow for such levels of intervention.
The way they are implemented now would be similar to only installing seatbelts in cars where the driver has already been in an accident. Similar sentiment was around when seatbelt laws were put in place, "I'm a good driver." but the seatbelt protects you from yourself crashing as well as when someone else crashes into you!
In the same way, breathalysers (ignition interlocks) for everyone wouldn't be "for you" as much as for everyone to prevent them from drinking and crashing into you.
I hadn't thought about widespread ignition interlocks, and obviously there would be a lot of public pushback, and it would be quite intrusive, but I could see it helping reduce traffic fatalities dramatically.
What I would support is a further reduction in the allowed BAC, and stricter enforcement of traffic laws in general.
How would you solve that? The FAA can issue all sorts of regulations requiring rest breaks, fatigue detection, etc. -- be sure you're ready for that level of intervention before you ask for this level of investigation.