The ladder sleeper developed by RTRI is a rail-support component for the next generation. The concept of floating ladder track is that composite rails are floated from the concrete track-bed by means of vibration isolators with a low spring constant. For high-speed rails, there are subjects to be solved in the floating ladder track. Namely, the propagation velocity of track deformation due to the low track stiffness impulsive wheel-load characteristics caused by wheel/rail irregularities must be investigated. The paper presents analytical and experimental results of these subjects.