Effects of induced travel due to capacity changes in tolled highways

Traditional traffic and revenue forecast showed a so-called optimism bias and one of the reason for this may be the failure to account for the induced traffic due to improvement on highway conditions or addition in lane capacity. While numerous studies have confirmed the existent of induced traffic, this study first critically reviewed and redefined the concept of induced travel that is appropriate for tolled highway analysis. A series of aggregated models and distributed lagged models were developed using 8-year time series data from 5 tolled highways from a second level province in the mainland China. Results showed that short run and long run elasticities of lane kilometer were around 0.25 and 0.96. The developed models were then used to project the traffic out for 5 years to investigate the impacts of growth in different variables on the total vehicle kilometres of travel (VKT). These results could provide a good reference for future tolled highway traffic and revenue forecasts.