1. Graduate Research Assistant, Dept. of Civil and Environmental Engineering, Univ. of Delaware, Newark, DE 19716.
2. Graduate Research Assistant, School of Civil and Environmental Engineering, Cornell Univ., Ithaca, NY 14852.
3. Professor, Dept. of Economics, East Carolina Univ., Greenville, NC 27858 (corresponding author).
4. Professor, Dept. of Civil and Environmental Engineering, Univ. of Delaware, Newark, DE 19716.
5. Professor, School of Civil and Environmental Engineering, Cornell Univ., Ithaca, NY 14852.