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The purpose of this research was to develop improved approaches to assessing the costs of urban traffic congestion and to make corresponding estimates of the costs of congestion in Auckland (New Zealand).

Various definitions of congestion were reviewed and it was found that the concept of congestion is surprisingly ill-defined. A definition commonly used by economists treats all interactions between vehicles as congestion, while a common engineering definition is based on levels of service and recognises congestion only when the road is operating near or in excess of capacity. A definition of congestion based on the road capacity (ie the maximum sustainable flow) was adopted. The costs of congestion on this basis are derived from the difference between the observed travel times and estimated travel times when the road is operating at capacity.

Estimates were made of the annual costs of congestion in Auckland, based on this definition and also relative to free-flow travel conditions. These estimates covered: the travel time and reliability differences for travel in peak periods; vehicle operating cost, environmental cost and crash cost changes associated with the differences in travel speeds; and schedule delay costs associated with travellers who adjust their time of travel to avoid the congested peak periods.

Erratum

24 May 2013

Page 57 - Table A.1: Summary of STCC estimates of Auckland recurrent congestion costs

Interpeak - Total annual costs ($ million) figure corrected to read 381.2

Keywords: (costs) of congestion, Auckland, New Zealand, speed-flow functions, (traffic) congestion