Oregon has relied on urban growth boundaries (UGBs) to contain growth in incorporated cities since it established a statewide planning program in 1973. Oregon state law requires that UGBs have enough land to accommodate 20 years of population and employment growth. Land inside the UGB is not immediately available for urban development until it is annexed and urban level infrastructure is available. This study focuses on policies and development patterns in the “urbanizable area”––land within the unincorporated areas inside the UGB that is reserved for future urban use. We examined planning documents, conducted GIS analysis, and administered a survey in 29 cities in five case study counties in Oregon. Our threefold analysis examined: (a) the agreements for managing growth in the urbanizable area; (b) trends in development and density in the urbanizable area, and (c) perceptions of managing growth from planning directors. Results show that development at low densities (around 1.5 dwelling units per acre) is occurring within the urbanizable area. These results have important implications for future development patterns and UGB expansions affecting rural areas. Low-density development inside the UGB may constrain available land supply, cause more frequent UGB expansions, and lead to noncontiguous, leapfrog development.

中文翻译：

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城市增长边界内的郊区增长？俄勒冈州城市发展考察

自 1973 年制定全州规划计划以来，俄勒冈州一直依靠城市增长边界 (UGB) 来控制合并城市的增长。俄勒冈州法律要求 UGB 拥有足够的土地以适应 20 年的人口和就业增长。UGB 内的土地不能立即用于城市发展，除非它被吞并并且城市层面的基础设施可用。本研究侧重于“可城市化区域”的政策和发展模式——UGB 内未建制区域内保留用于未来城市使用的土地。我们检查了规划文件，进行了 GIS 分析，并对俄勒冈州五个案例研究县的 29 个城市进行了调查。我们的三重分析审查了：(a) 管理可城市化地区增长的协议；(b) 可城市化地区的发展趋势和密度，以及 (c) 规划主管对管理增长的看法。结果表明，可城市化区域内正在发生低密度（每英亩约 1.5 个住宅单元）的开发。这些结果对影响农村地区的未来发展模式和 UGB 扩张具有重要意义。UGB 内部的低密度开发可能会限制可用土地供应，导致 UGB 更频繁的扩张，并导致非连续、跨越式发展。