This research reviewed the literature on traffic growth prediction in New Zealand and overseas, surveyed local traffic growth forecasting practice in New Zealand, reviewed the traffic growth procedures in the Project Evaluation Manual, and attempted to identify the factors that affect traffic growth and establish to what extent.

Although there is a demand locally for guidance in traffic growth prediction, there is no uniformity of approach by roading authorities and a lack of knowledge of how well the current methods work. More needs to be done in areas where growth is significant and/or land use is changing and driving traffic growth. Moreover, commercial freight traffic growth needs to be better modelled and predicted. Areas for further investigation include using a Bayesian method to predict growth, developing a national traffic growth forecasting programme, investigating the effects of capacity improvements and seal extension projects on traffic growth, and developing methods of forecasting local traffic growth by vehicle type and time period.