Freeway-related air pollution and its harmful health risks have been observed in recent research in the environmental-health sciences. In this study we investigate the impact of freeway and arterial-road air pollution on vulnerable populations—for example, the poor, minorities, children, and the elderly—whose housing options are limited. Because many mobile-source emissions decay rapidly with distance, approaching background concentrations at 330 ft from the freeway, populations living near limited access roads are most at risk from exposure. Furthermore, microscale air monitoring systems are rarely in place at these locations in the United States. In this research we will define freeway air-pollution sheds with the aid of a geographic information system analysis and determine populations that may be at risk from exposure to mobile-source pollutants in two West Coast metropolitan areas (Seattle and Portland). We then use cluster analysis to identify key neighborhoods at risk in Seattle. Subsequently, we apply a hedonic pricing model to understand the extent to which house price values in Seattle are related to freeway proximity. Finally, we discuss policy options, planning implications, and mitigation measures, including an assessment of air-quality monitoring needs and land-use prescriptions.