1. Assistant Professor, Dept. of Civil Engineering, Kangnung National Univ., 123 Jibyeon-Dong, Gangneung, Gangwon-Do 210-702, Korea. E-mail: swl@kangnung.ac.kr
2. Graduate Student, Dept. of Civil Engineering, Kangnung National Univ., 123 Jibyeon-Dong, Gangneung, Gangwon-Do 210-702, Korea. E-mail: boy2nice@kangnung.ac.kr
3. Chief Research Engineer, Korean Highway Cooperation, San 50-5, Sanchuk-ri Dongtan-myeon Hwaseong-si Kyunggi-do 445-812, Korea. E-mail: hansu@freeway.co.kr
4. Associate Professor of Civil Engineering, 201 Transportation Research Building, The Pennsylvania Transportation Institute at The Pennsylvania State Univ., University Park, PA 16802 (corresponding author). E-mail: sms26@engr.psu.edu