1. Loughborough Univ., Loughborough, Leicestershire LE11 3TU, U.K. (corresponding author).
2. Technische Universität München, Arcisstrasse 21, 80833 Munich, Germany.
3. National Technical Univ. of Athens, School of Civil Engineering, Dept. of Transportation Planning and Engineering, 5, Iroon Polytechniou Str., Zografou Campus, Zografou-Athens, GR-15773, Greece.