Heavy traffic causes depressions in the road. Water collects there and seeps into tiny cracks. Then it freezes, expands and makes the cracks bigger with every cycle.
It's also possible for potholes to form if the roads are continuously covered in snow that is compacted into ice. There is no direct damage from traffic. The expansion of ice creates tiny holes throughout the road.
Heavy traffic causes depressions in the road. Water collects there and seeps into tiny cracks. Then it freezes, expands and makes the cracks bigger with every cycle.
It's also possible for potholes to form if the roads are continuously covered in snow that is compacted into ice. There is no direct damage from traffic. The expansion of ice creates tiny holes throughout the road.