The vehicle chassis dynamometer recently selected by the EPA for its own research and testing programs is described. The design provides accurate electrical inertia and road-load simulation through a wide power range and eliminates the need for warm-up. The principal innovative features of this dynamometer are the central placement of an AC flux-vector power exchange unit (PEU) between the rolls of a single 48-inch diameter roll-set, the friction-compensated motorized roll bearings, and the unitary cast-iron frame. The dynamometer controller employs a feedforward algorithm that delivers an unusually rapid response to a step-change in load command. It employs two computers to carry out its control functions, to provide the operator with real-time test monitoring, and to perform a variety of automatic functions.