It has become well recognized that nonmotorized transportation is beneficial to a community's health as well as its transportation system performance. In view of the limited public resources available for improving public health and transportation, the present study aims to (a) assess the expected impact of built environment improvements on the substitutive, complementary, or synergistic use of motorized and nonmotorized modes and (b) examine how the effects of built environment improvements differ for different population groups and for different travel purposes. The bivariate ordered probit models estimated in this study suggest that few built environment factors lead to the substitution of motorized mode use by nonmotorized mode use. Instead, factors such as increased bikeway density and street network connectivity have the potential to promote more nonmotorized travel to supplement individuals' existing motorized trips. Meanwhile, the heterogeneity found in individuals' responsiveness to built environment factors indicates that built environment improvements need to be sensitive to local residents' characteristics.