Portland's urban growth boundary, adopted in 1979, separates urban areas (where high-density development is encouraged and focused) from traditional farm land (where restrictions on non-agricultural development are very strict). This was atypical in an era when automobile use led many areas to neglect their core cities in favor of development along interstate highways, in suburbs, and satellite cities. The original state rules included a provision for expanding urban growth boundaries, but critics felt this wasn't being accomplished. In 1995, the State passed a law requiring cities to expand UGBs to provide enough undeveloped land for a 20-year supply of future housing at projected growth levels.