Longitudinal Analysis of Transit's Land Use Multiplier in Portland (OR)

Problem, research strategy, and findings: We assess the direct and indirect effects on car use (as measured by household vehicle miles traveled [VMT]) of the Portland Westside Max light rail transit (LRT) extension. We use longitudinal data to estimate the effects of discrete changes in the built environment by comparing a treated transit corridor with a highway corridor that serves as a control. Before the LRT line, the transit and highway corridors were comparable in almost all respects, including household VMT. After the LRT line was completed, the transit corridor had higher density, generated significantly more household walk and transit trips, and experienced a slower rise in VMT per household. We estimate a transit multiplier of 3.04, meaning that transit reduces VMT by three vehicle miles in total for every vehicle mile reduced due to transit ridership. The direct effect occurs through increases in transit ridership and associated reductions in household VMT. The indirect effect is achieved primarily through increased walking around stations and secondarily through increased densities around stations. Fixed-guideway transit in tandem with comprehensive public policies that promote transit-oriented development (TOD) around transit stations on one hand, and highway corridors on the other, produce different transportation outcomes. Takeaway for practice: Building rail lines with supportive local government land use policies and local and even state investments around rail stations can slow the growth of auto use.