A truck or lorry is a motor vehicle designed to transport cargo. Trucks vary greatly in size, power, and configuration. Smaller varieties may be mechanically similar to some automobiles. Commercial trucks can be very large and powerful and may be configured to be mounted with specialized equipment, such as in the case of refuse trucks, fire trucks, concrete mixers, and suction excavators. In American English, a commercial vehicle without a trailer or other articulation is formally a "straight truck" while one designed specifically to pull a trailer is not a truck but a "tractor".Modern trucks are largely powered by diesel engines, although small- to medium-size trucks with gasoline engines exist in the US, Canada, and Mexico. In the European Union, vehicles with a gross combination mass of up to 3.5 t (3.4 long tons; 3.9 short tons) are known as light commercial vehicles, and those over as large goods vehicles.