a parking lot at one place i worked at had some freezing rain & snow conditions happen to it. parts of the parking lot were unsafe to walk on never mind try to park in at this point. one driver got stuck, not because the snow was too high but because when he would try to inch forward he would be headed sideways to one car, when he tried to go backwards he would slide sideways and nearly hit another car. he was not going more than a km, it was just that slippery. he had to be pushed out of the way by some people because he could not go forward or back out of the driving area of the lot, but conditions in that spot where he got stuck looked exactly the same as the rest of the lot that he was able to navigate freely... 20km is pretty slow (though some of the ice roads are slower), but you can still end up sliding around...