The purpose of this research was to investigate if and how systems dynamic (SD) modelling could be used for understanding traffic flows at an inter-regional (state highway) level, in the context of improving understanding of the relationship between economic activity, the demand for freight, and the performance of the rail and road network. We used the Auckland – Hamilton – Tauranga (AHT) triangle as a pilot case study.
The research involved the design and construction of three models; two simple Bayesian vector autoregressive model to forecast economic activity and freight flows within the AHT region, and a high level SD model for simulating freight flows along the main roads in the region. The key strength, and hence the main reason for selecting an SD model for this latter task, is that time is explicit. This means the SD model can simulate processes such as traffic flows, encompassing delays, congestion and capacity constraints.
The SD model can be used to ask ‘what if’ questions around future freight growth and infrastructure planning. Examples include road improvements along the Waikato Expressway and the Kaimai Range, greater use of larger (HPMV) trucks, changes in driver working hours and road–rail substitution.
Keywords: land use transport interaction (LUTI), model, scenario, system dynamics, vector autoregressive (VAR)