Gravel ballast is unable to maintain straight tracks when trains travel at high speed. Tracks become deformed and rocking motion sets in. Furthermore, when essentially identical trains travel at equal speed, tracks become distinctly wavy and trains rock in steady rhythms. While train wheel assemblies are physically forced to follow wavy tracks, their suspension springs can be augmented so that wavy motions are not passed upwards to passenger compartments. This is accomplished with computer controlled physical spring bypasses. Through instrumentation, computers read wave length and amplitude of snaking tracks, offset them by half a wave length and instruct the physical spring bypasses to respond in equal measure, thus canceling forces which cause rocking motions of passenger compartments.
US Patent 6, 122, 578