Why no focus on e.g. a top down federal "system" that would take over the driving e.g. just on the highways/interstates? Seems like that would be orders of magnitude EASIER.
Why not automate cargo ships? There's far less to hit in the ocean and far fewer inputs required.
Why still have human pilots in airplanes when they're largely automated?
Or use GPS to limit the speed of vehicles to the speed limit that's been set? For that matter why allow the sale of vehicles capable of exceeding 85 miles per hour (the highest speed limit anywhere in the country)?
To respond to your tangent: Breathalyzers are not all that reliable, nor is GPS localisation... And a national speed limit would mostly reduce revenue (not to mention the new problems regarding who is liable for maintaining the limit correctly). There is a great history of implementing practical safety requirements, maybe not the first globally, but when it becomes practical to adopt something we generally do.
Maneuvering a ship is but a very small part of all that's needed to maintain a ship operational – engine maintenance, paperwork, dealing with port agents and customs, operating the radio, etc.. Much of that can be automated, I'm sure, but the return on investment is quite poor. Crew salaries are a small part of all operations costs, so you're not saving much by removing them from the equation. (Add to that the fact that large cargo ships can exceed $1B worth of cargo, so I'm not surprised that the economics don't make much sense.)