This study examines how changes in built neighborhood environment (BNE) characteristics—such as land use diversity (HHI), dwelling density, intersection density, access to bike lanes, tree coverage, proximity to transit stops, parks, and sports centers, distance to water, and access to walkable destinations (e.g., retail)—influence Active Transportation (AT) following residential and job relocation. Using longitudinal data from 194 participants in the INTERACT project on the Island of Montreal, including 49 individuals who relocated homes and 68 who changed jobs, preliminary results indicate that simultaneous home and job relocation can positively impact AT levels. However, it is crucial to identify which specific BNE characteristics in the new location drive this change. We apply Generalized Additive Models (GAM) to capture nonlinear relationships and Structural Equation Modeling (SEM) to examine indirect effects through travel attitudes and mode preferences. Specifically, we assess whether relocating to neighborhoods with improved BNE characteristics leads to increased AT and whether shifts in preferred transportation modes mediate this relationship. The findings provide insights into how urban design interventions can promote sustainable mobility choices.