In the early 1970s, the principal platform for school buses smaller than conventional types but with more than 4 wheels was the truck chassis in widespread use for commercial delivery work: the step van. Essentially developed as a newer, larger generation of the Divco truck or IHC Metro van, the step van chassis was built with dual rear wheels and shipped to a body manufacturer with a bare frame. Often referred to as a "P-chassis", step-van chassis were produced by both Ford or General Motors.