Roads have a multitude of negative effects on wildlife, including bat casualties. Most bat species rely on life history traits characterised by high adult survival (associated with greater longevity) and low reproduction rates (hence slow population growth rates). Therefore, road kills are expected to negatively affect local abundance and bat population dynamics. Bat overpasses are among the proposed improvements intended to increase bat flight height to reduce collisions, but their effectiveness has rarely been tested. In this study, we performed a before-after analysis to assess the effectiveness of one bat overpass on bat flight height. We used a novel approach, the bat tracking toolbox (BTT), to reconstruct bat flight paths from thermal videos. We obtained 268 bat flight paths and our results showed that the flight height of bats increased significantly after the installation of the bat overpass. Considering that bat overpasses can help in some situations to increase habitat connectivity and reduce the collision risk, this mitigation measure needs to be further investigated in different contexts of road construction and/or road requalification.