Exploring thresholds of built environment characteristics for walkable communities: Empirical evidence from the Seoul Metropolitan area

•Test whether a non-linear relationship exists between the built environment and walking.•Positive association with density were greatly beyond 9132–16,101 persons/km2 of density.•The effect of land-use mixture and road connectivity sharply declined at a certain intensity.

Numerous studies have shown that dense, well-connected, and diverse environments are key features that promote walking. Accepting these finding as true, we hypothesized that decreasing marginal effects may occur in the associations between the built environments and walking. The purpose of this study was as follows: (1) to empirically test whether a non-linear relationship between the two exists, and (2) to identify the threshold of the built environment characteristics that promote walking. Using the 2012 Seoul Metropolitan Household Travel Survey, this study analyzed 411,899 individuals’ travel behaviors and their neighborhood environments. We calculated the population and street densities, and the Herfindahl–Hirschman Indexes (HHI) of 1107 administrative units located within the study area.The results of multilevel logit and linear models showed that these built environment characteristics had a non-linear relationship with the occurrence and duration of walking. The positive association with taking walking trips and negative association with taking private vehicle trips were greatly reduced where gross density reaches beyond 9132–16,101 persons/km2. The positive influence of land-use mixture and street connectivity also showed that the marginal number and duration of walking indicated a sharp decline at a certain intensity of those characteristics.The findings of the study imply that thresholds of density, street connectivity, and land-use mixture levels that promote walking may exist within the existing context of the study area. We hope that the findings of our study provide useful guidelines for those attempting to developing walkable communities by modifying the characteristics of the built environment.