Travel and air-quality benefits often are cited as among the many benefits of promoting smart growth. Through a recently released guidance, the U.S. Environmental Protection Agency officially acknowledged the role of smart growth in improving air quality and has offered three ways to account for air-quality benefits. The state of Maryland's effort--the first of its kind--to quantify travel and air-quality benefits in the state implementation plan (SIP) for air quality is presented. As one of the three demonstration projects in the state's smart growth and innovative SIP, the Digital Harbor is a collection of redevelopment and infill development projects in the areas surrounding Baltimore's harbor. These areas are historically Baltimore's base for manufacturing and port trade and are now being renovated and transformed into a hub for high-tech and tech-driven companies. Quantification of travel and air-quality benefits was conducted at two levels: at the macro level, a regional transportation model was used to evaluate travel and air-quality effects of these projects' central location; and at the micro level, the Smart Growth INDEX model was used to quantify travel effects and air-quality benefits of land use density, diversity, and design. Benefits were estimated through comparison of a smart growth scenario with two alternative growth scenarios. Subsequent model runs were conducted to examine the sensitivity of potential benefits to different combinations of land use density and land use mix. Policy implications are presented for the roles of planning and designing in achieving the goal of air-quality improvement.