Supposedly ice occurs only 1 percent of the time and studs provide a small improvement on ice while decreasing safety elsewhere.
But 1 percent of a three-month (90-day) winter is less than one day. Perhaps they mean that only certain spots (like bridges) are icy, but cars still must drive on them. In fact, precisely those spots are the most critical ones.
Links on the Washington State Department of Transportation website, and several other studies, found that studding provided a 10 percent to 15 percent improvement on ice and roughly a 5 percent loss in stopping power on non-icy roads.
These studies compared studs to the best non-studded tires only. But snow tires vary significantly. Consumer Reports magazine found over a 25 percent difference on ice between a poor snow tire and a good one. Studding the good one produced 14 percent improvement on ice. Studs improved the poor one a huge 44 percent, making it best of all.
Finally, one DOT-linked article stated that studs rough up icy spots, making them less hazardous for other traffic. Amazingly, Japan’s road maintenance antifreeze costs increased significantly after studs were outlawed.
Studs help when needed most.