Note that there are some non-powered tracked transports (i.e. trailers that roll on tracks rather than wheels), which have two idler wheels rather than a drive sprocket. There are also certain pieces of equipment, such as the Caterpillar D9 bulldozer (and numerous other Caterpillar brand bulldozers), Tucker Sno-cat and Mattracks rubber track conversion kits, which configure their tracks in the shape of a triangle, or pyramid (when viewed from the side), with the drive sprocket at the tip of the pyramid. In this configuration, there are two idler/roadwheels and one drive sprocket (as well as a number of small, load-bearing roadwheels). In very rare cases, the vehicle lacks an idler wheel at all; in Northern regions, one way people got better traction in deep snow was to take a simple three-axle truck, and install a simple continuous track around the rear wheels, thus forming a basic half-track system which featured two drive wheels, and no idler or road wheels. One almost never sees this on true tracked vehicles, however, as the second drive wheel is redundant.