Frost heaves occur when water gets under a road surface, freezes, expands and forces the road upward and cracks it open an inch or two at the peak. Frost heaves traditionally have a rise of 3-6 inches above the road surface and usually permanently damage it. Approaching frost heaves too fast encourage wrecks from sudden loss of control. Some roads and regions are subject to frost heaves. Hopefully signs are posted in those regions to warn you of the danger.