1. Dept. of Transport Science, KTH Royal Institute of Technology, Teknikringen 10, 100 44 Stockholm, Sweden (corresponding author).
2. Assistant Professor, Dept. of Transport and Planning, Delft Univ. of Technology, 2628 Delft, Netherlands; Dept. of Transport Science, KTH Royal Institute of Technology, Teknikringen 10, 100 44 Stockholm, Sweden.