This study is one of the first to test the effect of sidewalks on travel patterns and the first we know of to relate sidewalk availability with VMT (Vehicle Miles Traveled) and GHG (Greenhouse Gas) emissions. Recently, several large jurisdictions in King County have developed local sidewalk data layers, creating a new opportunity to look at pedestrian infrastructure alongside other investment and policy strategies associated with reduced VMT and CO2 (carbon dioxide). The study used travel outcome data from the 2006 PSRC (Puget Sound Regional Council) Household Activity Survey. The household-level analysis was restricted to households in King County cities where sidewalk data was already available, and modeled the association of urban form, pedestrian infrastructure, transit service and travel costs on VMT and CO2, while controlling for household characteristics known to influence travel.
The results provide early evidence in the potential effectiveness of sidewalks to reduce CO2 and VMT, in addition to a mixed land use pattern, shorter transit travel and wait times, lower transit fares and higher parking costs. However, the lack of ability to collect sidewalk data from across all of King County limited the study results. The sample population was lacking in variation and skewed towards the more urban and walkable parts of King County. This contributed to difficulties with multicollinearity in the modeling process, which in turn may have limited the significance of other urban form variables that have been repeatedly associated with travel outcomes in other King County studies. This study is, however, an important first step towards a more complete understanding of how pedestrian investment, urban form, transit service and demand management (pricing) policy can interact to meet the state’s goals for VMT reduction. The inclusion of sidewalk data from across the entire county or region will provide further, and more conclusive, insights.