Submitted on: 26 March 1998.
Revised on: 05 June 1998.
Accepted on: 14 July 1998.
___________________Journal of Transport & Health---ELSEVIER SCI LTD
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Submitted on: 24 October 2002.
Revised on: 30 December 2002.
Accepted on: 25 February 2003.
___________________Journal of Transport & Health---ELSEVIER SCI LTD
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Submitted on: 24 August 2004.
Revised on: 28 October 2004.
Accepted on: 04 December 2004.
___________________Journal of Transport & Health---ELSEVIER SCI LTD
Submitted on: 21 February 2008.
Revised on: 20 May 2008.
Accepted on: 11 July 2008.
___________________Journal of Transport & Health---ELSEVIER SCI LTD
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