Generated Traffic and Induced Travel - Implications for Transport Planning

They find the elasticity of VMT with respect to statewide road density is 0.019 in the short run and 0.093 in the long run (a 10% increase in total lane-miles per square mile increases state vehicle mileage by 0.19% in the short run and 0.93% in the long run); with respect to total road miles is 0.037 in the short run and 0.186 in the long run (a 10% increase in lane-miles causes state VMT to incr. [...] (US 1991 Dollars) Any incremental external costs of generated traffic should be included in project evaluations, “incremental” meaning the difference between the external costs of the generated travel and the external costs of alternative activities. [...] The incremental external costs of road capacity expansion tend to increase over time as the total amount of generated traffic grows and an increasing portion consists of induced motor vehicle travel and trips. [...] Failing to account for the full impacts of generated and induced travel tends to exaggerate the benefits of highway capacity expansion and undervalue alternatives such as transit improvements and pricing reforms (Romilly 2004). [...] (Based on the “Moderate Latent Demand” curve from Figure 3) The model divides generated traffic into diverted trips (changes in trip time, route and mode) and induced travel (increased trips and trip length), using the assumption that the first year’s generated traffic represents diverted trips and later generated traffic represents induced travel.