Zoning ordinances are supposed to embody a comprehensive plan for a community's future. The amount of land an ordinance allocates to different zones is based, in theory, on projections of future population and business growth. A basic level of community service is taken for granted in the new city although it is harder to achieve in older urban areas. At Laguna West, a planned community in Sacramento County, California, designed by Calthorpe, the commercial center is located on one side of the main arterial road. Calthorpe has done several regional planning studies showing how transit-oriented communities can be put in place along projected rail routes. Both the transit-oriented and traditional neighborhood design concepts have been written into zoning ordinances. Dade County, Florida, is among the jurisdictions that have adopted a Traditional Neighborhood Development District as an alternative to planned unit development. A specific plan is like a planned unit development in that an individual design can become the zoning.