National Geographic : 1974 Feb
Plowing into a Kansas dawn, the drivers keep alert for "black ice," a slippery sheet that glazes the road surface and can turn their 33-ton loaded vehicle into a jackknifing juggernaut. "We call it 'black' from the old days when most of the roads were macadam," says Paulson. "On concrete it looks gray. Even at five to ten miles an hour it can give you trouble."