Background:
In today’s society, air pollution and obesity pose two major threats to public health. One of the main causes for these two societal issues is the auto-dependent behavior of individuals. Policy makers around the world are seeking ways that would encourage people to drive less and walk/bike more. Many past studies in the areas of public health, planning, and transportation have pointed to built environment design as a potentially powerful intervention strategies to promote active living. But many have failed to recognize that a built environment change could lead to three different effects on travel behavior: substitutive (substituting driving with walking/biking), complementary (more walking/biking with no change in driving) and synergistic (more driving along with more walking/biking). Only the substitutive effect implies a win-win built environment improvement that would make people pursue more active transport (walking/biking) while at the same time cutting back on their car use. Such a win-win strategy would lead to increased levels of physical activity among people and create cleaner environments to live which ultimately translate to a better public health.
Objectives:
The purpose of this study is to identify and evaluate win-win built environment improvement strategies that would promote public health through both reduced driving and increased active transport. Specifically, the paper describes an econometric analysis framework capable of differentiating the built environment elements that result in substantive effect from those that lead to complementary or synergistic effects. It describes the application of this modeling method to identify the impacts of various built environment factors on individuals’ daily travel distances by motorized versus non-motorized modes. Furthermore, the paper presents a quantitative assessment of the economic return of promising built environment improvement strategies by estimating and comparing the associated health benefits against construction costs.
Methods:
The primary data source for this study is 2001 National Household Travel Survey (NHTS) add on sample from Dane County, Wisconsin. Various social and built environment measures were derived from US Census 2000 and geospatial data from the local planning agencies. Historic temperature and snow/rainfall data is obtained from National Climatic Data Center (NCDC) and used to control for weather factors. Neighborhoods for each sampled household are represented by one- and quarter-mile network buffers. Our econometric analysis account for several built environment measures such as land-use mix, retail accessibility, neighborhood socio-demographic composition, street connectivity, bike lane availability, and sidewalk prevalence. The econometric analysis employs the Spatial Seemingly Unrelated Regression model structure that accounts for spatial serial autocorrelation and intra-person correlation. The empirical model is used to analyze the travel impacts of hypothetical built environment changes. These travel impacts are then translated into health impacts and monetary values.
Results:
After controlling for various person and household characteristics, we found that built environment factors are strongly associated with travel behavior. The results indicate that increasing length of bike lane in neighborhood has complementary effect - that is, people would walk/bike more but would still continue to drive at the same rate. Two win-win strategies were found to give the substitutive effect. One is increased regional retail accessibility and the other is increased prevalence of sidewalks within 1 mile neighborhood buffers. Our benefit-cost analysis showed that, by an investment of around $450M that makes sidewalks available to all the residents in Dane County, the combined benefits from increased physical activity and reduced emissions is estimated to be around $91.65M per year. While concrete sidewalks have an expected service life between 20 and 40 years, our estimated benefit-cost ratio of 1.73 over a ten year life-cycle demonstrates sidewalk provision as a cost effectiveness and health-promotive investment.
Conclusions:
It was found that certain built environment measures can be used as an effective strategy to positively influence the travel behavior of people and the health of the community. Immense public health benefits gained by better air quality and increased physical activity were shown to outweigh the cost of implementing such built environment measures.
