1. Professor, Center for Transportation Research, Dept. of Civil Engineering, National Univ. of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Republic of Singapore (corresponding author).
2. Associate Professor, Center for Transportation Research, Dept. of Civil Engineering, National Univ. of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Republic of Singapore.
3. Research Engineer, Center for Transportation Research, Dept. of Civil Engineering, National Univ. of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Republic of Singapore.