This report examines the potential for synergistic emissions benefits for groups of projects funded by the Congestion Mitigation and Air Quality Improvement (CMAQ) program. The key issue being addressed is the extent to which multiple projects might have synergistic effects—i.e., the benefits of the whole set of projects being greater than the sum of the benefits of individual projects. The report: (1) provides information to support State and Metropolitan Planning Organization (MPO) investment and policy decisions involving multiple factors affecting transportation-related outcomes; (2) may be of value to State Departments of Transportation (DOT) and MPOs interested in conducting programmatic assessments of the set of CMAQ projects under review; and (3) lays a framework for testing suites of CMAQ projects for evaluating their combined or synergistic effects towards improving air quality and relieving congestion. The report describes benefits, challenges, and solutions in leveraging potential synergies among CMAQ projects. It provides grouping scenarios and sample menus of projects that might be expected to create synergies, for both metropolitan and statewide levels of application.
