1. Research Engineer, Korea Transportation Institute, 2311 Daehwa-Dong Ilsan, Seo-Gu, Geonggy-Do, Korea. E-mail: transdlm@gmail.com
2. Assistant Professor, Dept. of Civil and Environmental Engineering, The Pennsylvania State Univ., 223B Sackett Building, University Park, PA 16802 (corresponding author). E-mail: edonnell@engr. psu.edu