This is tragic and scary. I heard a report that they think the driver had fallen asleep at the wheel.
We had a similar near miss in Alaska 3 years ago following our cruise on the Mariner. My wife and I had just finished our Alaska cruise on the Mariner, and we were in a mini-bus with about 10 other people on our way from Seward to Anchorage. We were all pretty tired, so most of us were trying to get some sleep. One passenger in the back was awake and noticed us starting to weave and swerve on a windy section of road. He could see the driver was about to fall asleep and ran up to wake him up. The driver pulled over immediately and was very shaken - he seemed to be a combination of embarrassed and scared of what would happen (like if he would have a job tommorrow). We stopped for a while and he asked if we wanted him to keep driving. We decided he could drive the rest of the way since we were close and we didn't expect ANYONE would sleep the rest of the drive. We were all very grateful to that passenger who was paying attention.
Bill