drive in 1910. Soon after, most cars in the U.S. converted to left hand drive. Passenger cars Steering wheels for passenger automobiles are generally circular and are mounted to the steering column by a hub connected to the outer ring of the steering wheel by one or more spokes (single spoke wheels being a rather rare exception). Other types of vehicles may use the circular design, a butterfly shape, or some other shape. In countries where cars must drive on the left side of the road, the steering wheel is typically on the right side of the car (right-hand drive or RHD); the converse applies in countries where cars drive on the right side of the road (left-hand drive or LHD). In addition to its use in steering, the steering wheel is the usual location for a button to activate the car's horn. Modern automobiles may have other controls, such as cruise control, audio system, and telephone controls, as well as paddle-shifters, built into the steering wheel to minimize the extent to which the driver must take their hands off the wheel. The steering wheels were rigid and mounted on non-collapsible steering columns. This arrangement increased the risk of impaling the driver in case of a severe crash. The first collapsible steering column was invented in 1934 but was never successfully marketed. By 1956, Ford came out with a safety steering wheel that was set high above the post with spokes that would flex, but the column was still rigid. In 1968, United States regulations (FMVSS Standard No. 204) were implemented concerning the acceptable rearward movement of the steering wheel in case of crash. Collapsible steering columns were required to meet that standard. Before this invention, the Citroën DS incorporated a curved and off-center single spoke steering wheel designed to deflect the driver away from the steering column in case of a crash. Power steering gives the driver an easier means by which the steering of a car can be accomplished. Modern power steering has almost universally relied on a hydraulic system, although electrical systems are steadily replacing this technology. Mechanical power steering systems were introduced, such as on 1953 Studebakers. However, hydraulically assisted systems have prevailed. While other methods of steering passenger cars have resulted from experiments, for example the "wrist-twist" steering of the 1965 Mercury Park Lane concept car was controlled by two rings, none have yet been