IIUC it's mostly that speed limits are set a little conservative relative to average road conditions.
The tongue-in-cheek way it was explained to me once was "the highway isn't 70 because you need that. It's 70 because the trucker driving sleep-deprived in a light rain who doesn't know his left tire is about to blow needs that."
The tongue-in-cheek way it was explained to me once was "the highway isn't 70 because you need that. It's 70 because the trucker driving sleep-deprived in a light rain who doesn't know his left tire is about to blow needs that."