Seattle’s Green Housing Option: How ADU Production Can Reduce Reliance on Cars by Increasing Density in Single-Family Zones

Abstract

This study identifies the Seattle neighborhoods where accessory dwelling unit (ADU) production would reduce reliance on cars by increasing population density in single-family zones. Increased density would reduce greenhouse gas emissions from work and non-work related travel by providing the consumer base to support expansions to transit and attract local businesses. It identifies Seattle neighborhoods where population density is on the verge of crossing the car-reliance threshold, in addition to identifying the average Walk, Bike and Transit Scores across Seattle’s Census block groups to determine the extent of non-car travel options by foot, bike, public transit, and car share programs. This study reveals that density and access to non-car travel options are highest near Seattle’s economic hubs: Downtown, Capitol Hill, and University District. Moving toward the perimeter of the city resulted in lower density and less access to non-car travel options, where single-family zoning covers over half of the city. The Seattle neighborhoods where ADU production would shift reliance on cars to utilizing green transit options are Ballard, Greenwood, and Greenlake.