Tractor-trailers, also known as semi-trucks, can weigh more than 16 times the average passenger car. Semis are typically 53 feet long, 8 and a half feet wide, and over 13 feet high. They’re difficult to maneuver, require at least 350 feet to come to a complete stop, and often carry hazardous materials. A collision with a truck of this size can be disastrous, if not fatal.