1. Finnish Transport Safety AgencyP.O. Box 320FI‐00101HelsinkiFinland
2. Industrial Engineering and ManagementUniversity of OuluP.O. Box 4610FI‐90014Oulun yliopistoFinland
3. VTT Technical Research Centre of FinlandP.O. Box 1000FI‐02044VTTFinland
4. Civil Engineering Research Institute for Cold Region1‐3 Hiragishi, Toyohira‐kuSapporo062‐8602Japan