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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.

This research estimates commuting costs associated with Seoul's Greenbelt. It uses a density gradient framework for workers and residents and assumes that the Greenbelt results in a major discontinuity in these gradients that would be eliminated if the Greenbelt did not exist. This means abolition of the Greenbelt would result in both more workers and residents within the Greenbelt and fewer outside (both centrally and peripherally). The commuter distance savings from this reallocation form the basis for measuring the commuting costs. The average savings is 5 percent (a reduction from 7.14 km to 6.79 km); Greenbelt workers and residents would achieve substantial savings that are not fully offset by modest increases for those in the non-Greenbelt zones. Total commuting costs associated with the current Greenbelt are $65.96 million per year for out-of-pocket costs ($12.01 per commuter), or $395.56 million per year ($72.02 per commuter) including the value of travel time.Korea has had a Greenbelt policy in place since 1971, not as long as the United Kingdom but certainly long enough for the policy to be evaluated. Although the policy has been amended several times in minor ways over the years and has been the object of attack from many quarters in the recent past (Choi 1997), it was entrenched as the key element in Korea's land use controls until fall 1998, when plans were announced to modify the policy. Under the control of the Ministry of Construction and Transportation, although managed by local governments, it stands as a prime example of top-down centralized physical planning. It has made the life of local government officials much more difficult as they have had to cope with the pressures of rapid population growth and economic expansion in the face of severe land supply constraints (Bae 1998). The moves toward increasing local autonomy in recent years had negligible impacts on Greenbelt strategies, and the recent announcement appears to have been initiated by a top-down decision from the president. It has had severe adverse effects on land and housing values,We are grateful to the editors and anonymous referees for helpful comments in the revision of this article.

This article uses a specific and long-established planning policy, Seoul's greenbelt, to explore the concept of counterfactual planning. Suppose the greenbelt had never existed. How would the spatial structure of the metropolitan region have been different? Under both monocentric and polycentric assumptions, both population and employment (in terms of densities and numbers) would have been much lower in the core city and the periphery. The effects would have been more dramatic in the core city, suggesting that the greenbelt contributed significantly to densification and congestion. Still, its consequences for leapfrog development were far from negligible. In addition, because the greenbelt policy was reinforced by a strong government strategy to build very large new towns beyond the greenbelt, a significant jobs-housing imbalance resulted because people decentralized much faster than jobs. Whether these effects are offset by the recreational and other environmental benefits of the greenbelt is unclear.

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