1. Associate Transportation Researcher, Texas Transportation Institute, College Station, TX 77843 (corresponding author).
2. Director, Center for Air Quality Studies, Texas Transportation Institute, College Station, TX 77843.
3. Director, Traffic Analysis Section, Texas Dept. of Transportation, 118 E. Riverside Dr., Austin, TX 78704.
4. Assistant Professor, Zachry Dept. of Civil Engineering, Texas A&M Univ., College Station, TX 77843.