1. Professor, Center for Transportation Research, Dept. of Civil Engineering, National Univ. of Singapore, 10 Kent Ridge Crescent, Singapore 119260.
2. Associate Professor, Center for Transportation Research, Dept. of Civil Engineering, National Univ. of Singapore, 10 Kent Ridge Crescent, Singapore 119260.
3. Research Assistant, Center for Transportation Research, Dept. of Civil Engineering, National Univ. of Singapore, 10 Kent Ridge Crescent, Singapore 119260.