1. Centre for Railway Research, Nihon University, Tokyo 102-0074, Japan
2. Department of Mechanical Engineering, Graduate School of Nihon University, Tokyo 102-0074, Japan
3. Kyosan Electric Mfg. Co., Ltd., Yokohama City 230-0031, Japan
4. National Traffic Safety and Environment Laboratory, The National Agency for Automobile and Land Transport Technology, Tokyo 182-0012, Japan