Fiducials don’t need to be ON the road. They can be on signage or whatever. But fiducials are cheap. Just paint. (And you can, in fact, draw them by hand using a ruler, a square, and patience.)

They are error-detecting and error-correcting digital signage that gives you precision 6dof orientation “for free.” (And you can do even better... can stick a bunch of them all over a deformable object to map back the shape and deformation.... without lengthy registration and with only a single camera... unlike vidicon) And they’re easy to implement in software. Can be extremely fast (<10ms... no real limit as you can implement it in an FPGA) and fairly lightweight and can use basically any kind of digital camera (good or bad).

Are there such fiducials+libraries available today?

You can use almost any 2D matrix barcode as a fiducial, and those include error correction/detection already. Signing it would be easy.

I’m familiar with ARUCOs, but in my experience they tend to be somewhat finicky (Eg: mid-identified with a little bit of noise or unfavorable lighting), and accurate poses tend to require a lot more fiducial markers than might be considered “reasonable”.

The standard Aruco library in openCV is not the most stable fiducial tracking. But there are lots to choose from

Hello from Montreal, a city that is booming where you can't go a block without hitting a giant hole in the road or a bridge that's about to collapse. Having proper lines painted is pretty far along our hierarchy of needs. That said, I can easily imagine machine readable markers leapfrogging most of the existing infrastructure deficit.

It's easier to get money for a futuristic sounding project than for routine shoring up of infrastructure so it doesn't keep falling apart. (Just like many codebases)