Abstract: An apparatus controller for prompting a rider to be positioned on a vehicle in such a manner as to reduce lateral instability due to lateral acceleration of the vehicle. The apparatus has an input for receiving specification from the rider of a desired direction of travel, and indicating means for reflecting to the rider a propitious instantaneous body orientation to enhance stability in the face of lateral acceleration. The indicating may include a handlebar that is pivotable with respect to the vehicle and that is driven in response to vehicle turning.