In the UK when approaching a bend in the road a chevron sign warns you of the danger ahead. The problem is if you are not familiar with that road the bend could range from almost 180 degrees to just a mild curve. If the chevrons were replaced with a true image of the bend and possibly the angle it would prevent many accidents. The extra cost would be negligible.
I like your idea! But instead of a graphic of a bend why not have coloured reflectors in the chevron board to indicate the degree of severity, ie., Red for a sharp bend, amber for a moderate one and green or blue for lesser bends in the road.