1. University of Pretoria, Lynnwood Road, Hatfield, Pretoria, South Africa 0002.
2. Division of Research and Innovation, and Division of Transportation Planning, California Department of Transportation, Sacramento, CA 95811.
3. Built Environment, Council for Scientific and Industrial Research, P.O. Box 395, Pretoria 0001, South Africa.
4. Pavement Research Center, Institute of Transportation Studies, University of California, Berkeley, Berkeley, CA 94720.