National Center for Sustainable Transportation

The California Air Resources Board (CARB) has developed quantification methods to provide project-level greenhouse gas (GHG) and co-benefit estimates for administering agencies to use when selecting projects for funding from California Climate Investments programs. To measure GHG emission reductions from transportation projects, CARB relies on a method it published with the California Department of Transportation (Caltrans) in 2005 for evaluating motor vehicle fee registration projects and congestion mitigation and air quality improvement (CMAQ) projects, specifically transit and connectivity (TAC) features. This report addresses whether and how CARB might update two adjustment factors in the TAC methods that apply to transit facility and/or service expansion projects. The first factor is used to account for transit dependency in estimating ridership gains from a new transit project, by indicating the share of new riders who could be expected to have driven in the absence of the project. The second factor is a required input for the estimated length of an average unlinked transit passenger trip associated with a proposed transit project. This report also summarizes recent research on factors that influence transit ridership and dependency, to inform an understanding of how these factors may influence California Climate Investments programs. Results from the literature review are described in greater detail in the accompanying technical report.

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