Friction from passing car and truck tires warms the road surface and delays accumulation of snow. Also, auto exhaust warms the air above the road, which in turn warms the surface. In addition, state and local road crews often pre-treat the main roads ahead of a storm, which keeps them less snow-covered as a storm moves-in. In fact, trace amounts of road salt and other melting materials used for previous storms may still be left on the road to help prevent new accumulations as a second storm arrives.
---David Murphy
