Who makes America's semi-trucks

Nearly every product Americans touch is carried at some point by a truck. There are about 4 million Class 8 trucks on the road. Four manufacturers dominate this market. Daimler Trucks is the biggest, through its Freightliner brand. Daimler has about 40 percent market share. Upstarts are boldly promising to deliver electric semi trucks and autonomous driving systems. But some industry analysts say there is not a clear business models for a lot of these innovations yet in long haul trucking.