Willow Ptarmigan (Lagopus lagopus) races across the road in Denali National Park.  We saw several groups of these birds hanging out along the side of the road - in about the same spots at the same times of day - every day in Denali. When a bus or car approached the Ptarmigan would bolt across the road one by one.  They'd wait there for a while before doing the same thing on a return trip back across the road.  For such a plump bird they are surprisingly fast.  Must be those HUGE feet!