[1] Heriot Watt Univ, Sch Built Environm, Sir William Arrol Bldg, Edinburgh EH14 4AS, Midlothian, Scotland
[2] Loughborough Univ, Sch Civil & Bldg Engn, Transport Studies Grp, Loughborough LE11 3TU, Leics, England
[3] Univ Leeds, Inst Transport Studies, Leeds LS2 9JT, W Yorkshire, England