1. a Safety and Health Assessment and Research for Prevention Program, Washington State Department of Labor and Industries , PO Box 44330, Olympia, WA, 98504–4330, USA
2. b University of Michigan Transportation Research Institute, The University of Michigan , 2901 Baxter Road, Ann Arbor, MI, 48109–2150, USA
3. c Department of Industrial and Operations Engineering , The University of Michigan , 1205 Beal Avenue, Ann Arbor, MI, 48109–2117, USA