My car shows the speed limit of roads it knows. It uses GPS and stored limits. It also doesn't know the limits of non-major roads and doesn't attempt to show a limit then. My car is a 2013, and I've not paid the $$ to update the maps in that time (seriously, they want $200-$400 to update the maps).

Since I bought my car, Illinois (where I live) has raised the maximum limit on interstates by 10 MPH. My car doesn't know about it. If my car limited me to what it thought the limit was, I'd probably be driving 20 MPH slower than prevailing traffic, a decidedly unsafe situation.

The rental car I am using now certainly a) reads road signs for speed limit information, b) is definitely fooled by signs on off ramps etc.

It’s hard to imagine how speed limit systems would work without some sort of vision capabilities — a database of speed limits would never be up to date with roadworks and so on.

Nobody should be using autopilot driving through roadworks anyways.