The caterpillar has an interesting paint job.
Almost every large roller coaster has a three wheel assembly with wheels above, beside, and below the track. One set of wheels is above the track and they are usually called running wheels or tractor wheels. Another set of wheels, the side friction wheels, run along either the inside or outside lateral edges of the track. Side friction wheels keep the train centered on the track. For safety reasons, the underfriction, or up-stop wheels, are under the track and prevent the cars from lifting off the track during negative-g forces. But because this family coaster is so mild and takes turns so gently, the running wheels have flanges that curve around the metal rails. These flanged wheels are enough to turn the train.
©2015 Joel A. Rogers.