You would mainly see this at highway projects such as adding lanes or widening a bridge. They mainly carry tools, cones, and signs to and from large sites. Alot of them have a large sand bag type box at the back that can be lowered down when it is at a construction site. It looks like this: That yellow thing in the back is full of sand, If a car were to ram into it, the driver of the car would be safe. That was put into place by Caltrans because so many people would hit that truck and the top of their car would be destroyed be the overhanging bed in the back. It can be lowered and raised depending on if it is at a site or not. When raised, you'll notice a large white sign on the underside of all of these trucks stating; "Thank you for driving safely".