The Mountain Line Downtown Connection Center redefines sustainable public infrastructure in Northern Arizona. Built on an underutilized infill site at the edge of historic downtown Flagstaff, the project demonstrates how integrated planning and design can deliver high-performance sustainability, resilience, and equity—while remaining a responsible investment of public funds. The Center is the first commercial project to earn Gold certification under Coconino County’s Sustainable Building Program and the first contemporary mass timber project in Northern Arizona, reducing embodied carbon by more than 30 percent. A fully electric facility with rooftop solar achieves a 60 percent reduction in energy use intensity, with a pathway to net-zero energy. Through universal design, water-efficient landscaping, healthy building strategies, and community-driven public art, the Downtown Connection Center stands as a model for climate-responsive, people-centered transit infrastructure.