1. Centre for Industrial Management/Traffic and Infrastructure; KU Leuven; Celestijnenlaan 300A Leuven 3001 Belgium
2. Department of Mathematics; KU Leuven; Celestijnenlaan 200B Leuven B-3001 Belgium
3. School of Mechanical Engineering; Dedan Kimathi University of Technology; P.O. Box 657-10100 Nyeri Kenya