Even though the ice layer is very thin it is as slippery as any other, and unless the light shines at a low angle to make for glare it is invisible. People hit the ice and slide. The speed limit on the interstate is 80 mph ( which means 85) and hitting black ice on a curve can ruin your whole day if not the few minutes that are the rest of your life. Maybe mine, too, if I am next to the slider.