Roll-on/roll-off (RORO or ro-ro) ships are cargo ships designed to carry wheeled cargo (such as cars, trucks, semi-trailer trucks, trailers, and railroad cars), that are driven on and off the ship on their own wheels. Also a platform vehicle such as a self-propelled modular transporter can be used. This is in contrast to lift-on/lift-off (LoLo) vessels, which use a crane to load and unload cargo. RORO vessels have either built-in or shore-based ramps or ferry slips that allow the cargo to be efficiently rolled on and off the vessel when in port.