25 percent or the 75 percent target because doing so prevents much less land from being used for development than curtailing development in the lowest-density tracts where the average acres per DU are largest. Pursuing the latter strategy—eliminating all new development in tracts with densities below 1 DU per acre—results in achieving not only the 25 percent but also the 75 percent target. The reason is the large amount of acreage in the below-1-acre category (see the baseline in Table C-5). Because such large lots represented approximately 75 percent of the residential land developed between 1990 and 2000, this strategy would require an almost complete reversal of recent development patterns. Given the large amount of land available for development and lax land use policies in more rural counties, achieving such a goal would require extraordinary changes in land use policy and market trends.

The analyses provided here suggest that both the 25 and the 75 percent targets represent a significant departure from recent trends, which have involved lower densities than the average for new development over the decade of the 1990s and for decades before that. Doubling the density of 25 percent of new development by 2050 will not raise densities above the current average and will raise them only about 7 to 11 percent above the 2050 baseline. In addition, precedents for such changes in density can be found even in growing areas such as Phoenix. Nevertheless, Phoenix is not typical of many growing metropolitan areas, and meeting the 25 percent target will require a trend change. Doubling the density of 75 percent of new development by 2050 will require densities above those of existing developments, significantly above (approximately 20 to 33 percent) the 2050 baseline.

The committee disagreed about the feasibility of doubling the density of 75 percent of new development, even by 2050. Those members who thought it was possible questioned whether densities will keep declining. The combination of macroeconomic trends—likely higher energy prices and carbon taxes—in combination with growing public support for strategic infill, investments in transit, and higher densities