I build these car haulers with hardwoods like hickory, cherry and oak. The semi and trailer carry 6 cars that can be taken off and played with individually. The entire unit measures about 38 inches long, 6 inches wide, and 8 inches high. All the wheels roll and there's a holding peg in the back that keeps the cars in place so they don't fall out/off. I finish it with child-safe clear material. Each of the cars is approximately 4 inches long, 2 inches wide and 2 inches high. It's a real kid-pleaser because there are so many moving parts and because it will provide hours of imaginary fun.