1. Specialist, Div. of Statistics and Scientific Computation, Univ. of Texas at Austin, 2.104A WCH Building, 1 University Station, G2500, Austin, TX 78712 (corresponding author).
2. Credit Policy and Risk Analyst, HSBC, 26525 N. Riverwoods Blvd., Mettawa, IL 60045.
3. Professor, Center for Transportation Research, Univ. of Texas at Austin, 6.904 ECJ Hall, 1 University Station, C1761, Austin, TX 78712.
4. Associate Professor, Center for Transportation Research, Univ. of Texas at Austin, 6.204 ECJ Hall, 1 University Station, C1761, Austin, TX 78712.