The single biggest difference between Yellowstone in the winter and other seasons is the huge difference in the number of visitors. This is the main road between Mammoth Hot Springs and Old Faithful. The road isn’t plowed: the snow is packed and groomed and traffic is restricted to snow coaches and guided snowmobiles. During the summer you would be run over if you stood in the middle of this road to take pictures. During the winter you can enjoy the solitude and silence.