School bus, semitrailer collide in Wisconsin

A semi-truck slammed into the back of a school bus that had stopped to drop off students along a highway on Friday afternoon, seriously injuring five people.

[Wiley]

Quote: "He said investigators think the trucker did not see the bus. There were no skid marks where the accident happened about 3:40 p.m. just over a rolling ridge on state Highway 50."

Question one - what was the posted speed limit?
Question two - what was the sight distance from the top of the ridge to the point of impact?
Question three - what was the minimum stopping distance from the first point of view over the ridge to the point of impact?
Question four - given the above could the truck have safely stopped or had the school district established an unsafe stop?