In 1976 the author presented an SAE paper on ride quality in which a two-degree-of-freedom ride quality simulation was developed for measuring vertical motions. The present paper reports on the work done since that time. Side-to-side motion has been added to the simulator developed for the Association of American Railroads as well as the studies needed to find the impedance of humans when subjected to side-to-side and fore-and-aft motion. These studies found that rough rides are better endured during warmer weather and that women do not resonate as readily as men at the two critical and annoying side-to-side frequencies. Last, the paper deals with the use of a rigid mass to measure seat acceleration. Through a transfer function, a computer simulation has been developed to find the vertical seat acceleration.