The US, for various reasons that primarily relate to privatized healthcare and a proliferation of lawyers, had absurdly high rates of lawsuits and liability around driving. Most road signs here are excessive for the purposes of making it as straightforward as possible to assign liability to a driver in the event of an acccident.
A prime example of this is the "No U-Turn" signs all over the US. People make U-turns at these spots all the time. The sign is really just there to ensure that any accident resulting from said U-turn is always, no matter what, the turner's fault in a legal sense.
I'd be far happier if we were just allowed to ignore the signs and have strict liability for the consequences if we screw up doing so. Being subject to fines and harassment by law enforcement is what I don't like.
a) That's possible depending on how you quantify ability because average is influenced by outliers.
b) Is that supposed to be a rebuttal or something? I think "do whatever but strict liability if you F up" would be fine even for average and below average drivers. That's mostly how things already work in practice.
A prime example of this is the "No U-Turn" signs all over the US. People make U-turns at these spots all the time. The sign is really just there to ensure that any accident resulting from said U-turn is always, no matter what, the turner's fault in a legal sense.