The Sightline Institute has released a new study that compares exurban development over the last 20 years in the Portland, Oregon metro area with that of neighboring Clark County in Washington. (Exurbs are those developed areas just beyond suburbs and, in this case, outside of urban growth boundaries.) 

Both Clark County and the Portland metro area have comparable land use laws to restrict development outside of urban areas, but the study finds that Clark County had far more growth outside of its urban areas during that time period than did any of the studied Portland area counties, i.e., Washington, Multnomah, and Clackamas. One factor to consider is that Clark County’s growth-management rules did not take full effect until the mid-1990s. So, the study speculates, that probably accounts for some of the difference. Even so, between 2000 and 2010, when all of the areas should have been more-or-less on par with each other, Clark County’s exurbs and rural areas still added far more new residents than the Oregon counties studied.

Between 2000 and 2010, exurban housing grew 18% in Clark County, while it grew just four to five percent in Clackamas, Multnomah, and Washington Counties. One explanation given in the study for that disparity is that there may be differences between how land use and zoning policies are designed and enforced between the Portland metro and Clark County sides of the river.