You can get into very serious trouble on any one of them. And, you don't have to anything wrong or stupid either.

At a company I worked for a number of years ago, one of our drivers was maintaining a nice, slow, safe speed going down Donner into NV. But, the guy coming down behind him was out of control. Our trailer was instantly shortened up, the roof was blown up, and a good share of the load (boxes of paper) was launched into the air. The other driver was flown to a hospital. And, of all things... CHP made a comment about IMPEDING THE FLOW OF TRAFFIC...

Our driver ended up down next to the Truckee river.