Forecasting VMT response to roadway network changes in rural areas

Summary

How much roadway usage should be expected following freeway expansion in rural areas? This question has immediate application in a number of planning areas in the Minnesota Department of Transportation (MnDOT), and has not been widely studied in previous research, which has tended to focus on urban area vehicle miles traveled (VMT). In the current absence of a statewide travel demand model, MnDOT has little quantitative expectation of how roadway projects, including lane additions and interchange conversions, will change VMT, if at all. To address the gap, we developed two distinct methods for expectations of vehicle miles traveled (VMT) on rural Minnesota roadways, a network-based traffic assignment model and a statistical model of elasticities accounting for induced demand. Using each method we fit plausible models of the relationship between rural population, trip making, and the availability of lane miles in functional classes 1 - 5 (interstates to major collectors). Each approach forecast responses to network change in case studies of upcoming MnDOT projects, and strengths and weaknesses were compared. We provide a recommendation for elasticity values in calculating expected increase in VMT from capacity expansion, narrowing the expected guidance and making it more appropriate to rural Minnesota.