1. Professor and William J. Murray Jr. Fellow, Dept. of Civil, Architectural and Environmental Engineering, The Univ. of Texas at Austin, 6.9 E. Cockrell Jr. Hall, Austin, TX 78712 (corresponding author).
2. Graduate Transportation Engineer, Wilbur Smith Associates, 55 Public Square, Suite 600, Cleveland, OH 44113-1901; formerly, Graduate Student Researcher, The Univ. of Texas at Austin, 6.9 E. Cockrell Jr. Hall, Austin, TX 78712.
3. Graduate Student Researcher, Northwestern Univ..