1. Rotterdam School of Management and Erasmus Center for Optimization in Public Transport, Erasmus University, Rotterdam 3062PA, Netherlands;
2. Institute for Road and Transport Science, University of Stuttgart, Stuttgart 70569, Germany;
3. Econometric Institute and Erasmus Center for Optimization in Public Transport, Erasmus University, Rotterdam 3062PA, Netherlands;
4. Process Quality and Innovation, Netherlands Railways, Utrecht 3511 ER, Netherlands