These conditional urban developments do not include land-use zones but must provide their own infrastructure and basic services (SERPLAC Santiago, n.d.). The primary exception to restrictions on building outside of the urban boundary is found in Article 55 of the General Law of Urban Development and Construction (Ley General de Urbanismo y Construction), which allows certain land uses outside urban boundaries, including social housing, services, infrastructure and industrial uses. For example, the current system of zoning has been seen as an obstacle for new development, and zones tend to become obsolete more quickly than PRs are renewed (Peterman, 2008). Others have indicated that the zoning system limits opportunities to redevelop under-utilised areas within urban boundaries for new types of uses, such as multi-family housing (Trivelli, 2011). The pressure to develop beyond the urban boundary has contributed to the rise of conditional urban developments in the Santiago Metropolitan Region, which may undermine city-wide urban development strategies (Trivelli, 2011).