Napartaq, there are not always alternative routes available, and I was first and foremost thinking of exactly the examples you mention, accidents --- or to be precise, the foot-dragging "investigations" by the police of such accidents --- on the (extra-urban) Seward and Glenn Highways that in recent years tie up traffic for many hours at a stretch.  We have seen examples of exactly that on both highways in the vicinity of, but outside, Anchorage at least once this year already.  

I can remember one accident investigation (not the accident itself) on the inbound Glenn earlier this year that had traffic gridlocked for over six hours, with a number of those drivers meanwhile having run out of gas and further complicating the situation.  Again, these excessively long delays in clearing accidents from the roads are something which has never occurred until recent years, and which I find inexcusable and unacceptable, as should we all.