1. Metropolitan Washington Council of Governments, 777 North Capitol St., NE, Suite 300, Washington, DC 20002.
2. Charles Pankow Professor, School of Civil Engineering, 550 Stadium Mall Dr., Purdue Univ., West Lafayette, IN 47907-2051 (corresponding author).
3. School of Civil Engineering, 550 Stadium Mall Dr., Purdue Univ., West Lafayette, IN 47907-2051.