What if someone redraws road lines (or fakes the speed limit signs or whatever) to confuse drivers today?

With machine-readable signage based on fiducials, not only can you error-correct the signage (making it highly resistant to simple alterations and ambiguous readings), you can also encrypt it and get 6 degree of freedom vehicle vs signage pose information. All from a single camera view. That makes it MUCH more resistant to abuse than machine-learning of human-readable signage... arguably more resistant to abuse even than human readable signage is to humans.

(Also, I’ve thought of additional ways that fiducials could be resistant to such measures.)

What happens today when some kids move road cones so they point to oncoming traffic as a prank? You can have a car react the same way I did in that situation - slow down, take in the entirety of the situation ("cones say X, but that leads you into oncoming traffic") and ask the operator for directions or maneuver accordingly.

Just because some Teslas are dumb enough to drive into barriers today doesn't mean we can't continue improving the technology.

You’re actively paying huge dollar figures to experiment with your survival. Which I don’t judge even if I find it too risky for my taste. But your giant expensive experimental hunk of alloys and minerals is also a death sentence for others when it messes up.

Which is why we should use something less experimental and black-boxy than machine learning and more verifiable and robust like fiducials. (Regardless of whether we're talking about using machine vision for attempts at "self-driving," autopilot, or just driver safety features like lane-keeping or auto-braking or automatic speed limit reading.)

I mean you’d hope that self driving cars had a certain amount of error correction and weren’t just looking at one data point...

Hope is not a great thing to depend on when it comes to multi-ton fast moving objects