1. Dept. of Applied Mechanics, Chalmers Univ. of Technology, SE-412 96 Gothenburg, Sweden (corresponding author).
2. Professor, Researcher, Swedish National Road and Transport Research Institute, Box 8072, SE-402 78 Gothenburg, Sweden.
3. Senior Lecturer, Head of Civil Engineering Dept., Dept. of Civil Engineering, Chalmers Univ. of Technology, SE-412 96 Gothenburg, Sweden.