Proceedings of the 2015 Transportation Research Board 94th Annual Meeting (Paper 15-4940)
As decision-makers increasingly embrace life-cycle assessment (LCA) and target transportation services for regional environmental goals, it becomes imperative that outcomes from changes to complex systems are accurately communicated. California’s greenhouse gas (GHG) reduction policies have created interest in better understanding how public transit systems reduce emissions. An LCA is developed of the Los Angeles Expo line and a competing car trip that includes vehicle, infrastructure, and energy production processes, in addition to propulsion. Energy use, GHG emissions, and the potential for photochemical smog formation and respiratory impacts are assessed. When results are normalized per passenger kilometer traveled (PKT), life-cycle processes increase impacts by up to 83% for energy use and GHG emissions, and up to 690% for smog and respiratory impact potentials. However, the use of a non-time-based PKT normalization obfuscates a decision-maker’s ability to understand whether the deployment of a transit system reduces emissions below a future year policy target (e.g., 80% of 1990 emissions by 2050). The year-by-year marginal effects of the decision to deploy the Expo line are developed including reduction in automobile travel. The time-based marginal results provide clearer explanations for how environmental effects in a region change and the critical life-cycle processes that should be targeted to achieve policy targets. The line can be expected to breakeven on GHG emissions within two decades but its ability meet long-run policy targets is most sensitive to infrastructure construction emissions, mode shifting, a changing electricity mix, and improving automobile fuel economy.