Does compact development increase car use among car users?

One of the goals of compact urban development is to reduce driving and increase the use of sustainable modes of transportation (public and active transport). Nonetheless, the reduced travel distances associated with compactness may lead to two potential outcomes for car users: encouraging them to increase the use of sustainable forms of transportation or encouraging them to increase car trip frequency. We analyze car users in Montreal, Canada, from two perspectives: 1) “observed car users”, who made at least one trip using a private car on the day of the survey and 2) “potential car users”, who hold a driving license and reside in a household with a private vehicle, regardless of whether they used it on the survey day. To assess the impact of urban compactness on car trip frequency, sustainable trip frequency, and Vehicle-Kilometers Traveled (VKT), we conduct two distinct analyses—one for observed car users and another for potential car users— using instrumental variable regression. We find that though compactness marginally increases car trip frequency among observed car users, their overall car use is substantially decreased. A 10 % increase in compactness results in a 0.62 % marginal increase in observed car users' auto trips, 26 % substantial increase in sustainable mode trips, and 10 % decrease in VKT. A 10 % increase in compactness results in a 3.2 % reduction in potential car users' car trips, 25 % increase in sustainable mode trips, and a 14 % reduction in VKT. The findings' policy implications for accomplishing sustainable mobility, Montreal's target for 2050, are discussed.