Boxes or wheels: types of systems 137 3.6 Vehicles SNG vehicles can be built on a variety of types of base vehicles such as towed trailers, estate cars, SUVs, MPVs, pick-up vehicles, panel vans, box-body vehicles and even combined tractor units for towing pro- duction trailers. The majority of SNG vehicles are constructed on a vehicle or van between 3500 and 7500 kg (7700 and 16 500 lb) GVW (gross vehicle weight) in Europe, and up to 26 000 lb in the US, though as can be seen in Figure 3.17, systems are often fitted to smaller vehicles.