Where highways and freeways end abruptly with slow curves or a traffic light, they usually put up large yellow warning signs on both sides of the road, which are illuminated at night and have bright flashing lights so you can see them a mile away.

Is there some reason they can't do something like that where 501 crashed, or maybe a permanent yellow, rather than relying on the engineer seeing a small dark speed limit sign?

It seems obvious there should be a conspicuous warning of a slow curve.