Greenhouse Gas Emissions Inventory from Construction of Washington State Department of Transportation Roadways, Final Report

Abstract

Recent emphasis on actions to reduce large-scale greenhouse gas (GHG) emissions has pushed most state departments of transportation (DOTs) to develop carbon accounting practices compatible with their current standard data collection and storage practices. In particular, with the recently passed Buy Clean Acts in California, Colorado, and Oregon and the recently proposed Buy Clean and Buy Fair Washington Act, common construction materials such as cement concrete, steel, and asphalt are now under special attention. Once accurate and reliable accounting of GHG emissions is established, strategies can be formed that would help mitigate the adverse environmental impacts of materials utilized by state DOTs. This project, in collaboration with the Washington State Department of Transportation (WSDOT), is an attempt to perform a life cycle assessment (LCA) on some of the agency-wide operations that emit GHGs. To date, WSDOT has not conducted a comprehensive assessment on the embodied carbon of its construction material usage (i.e., upstream Scope 3 emissions inventory) with most previous carbon accounting practices being focused on Scope 1 and Scope 2 emissions (i.e., the carbon footprint of direct and indirect energy usage). Although several strategies are now in place to cut Scope 1 and 2 emissions, such as the use of alternative and renewable energy sources, strategies to reduce Scope 3 emissions have neither been fully recognized nor quantified. Therefore, this project uses several data sources from WSDOT in conjunction with lifecycle emission factor data to estimate GHG emissions from the materials used to build and maintain roadways under WSDOT’s jurisdiction. We found that upstream Scope 3 emissions for WSDOT as an agency contributes to more than half of its currently tracked total GHG emissions inventory by a five-year average of 310 thousand metric tons of CO2eq. This project further suggests carbon reduction targets for WSDOT and uses decarbonation scenarios to provide recommendations to achieve GHG reduction targets of 50% below the 2020 baseline in 2030 and 90% below the 2020 baseline in 2050.