1. Postdoctoral Fellow, Center for Transportation Research, Dept. of Civil, Architecual and Environmental Engineering, Univ. of Texas at Austin, Austin, TX 78712.
2. Graduate Student, Dept. of Mechanical Engineering, Univ. of Texas at San Antonio, San Antonio, TX 78249.
3. Professor, Dept. of Civil and Environmental Engineering, Univ. of Texas at San Antonio, San Antonio, TX 78249.
4. Assistant Professor, Dept. of Civil and Environmental Engineering, Univ. of Texas at San Antonio, San Antonio, TX 78249 (corresponding author).