Using a modified stepped-wedge randomized controlled trial to evaluate effectiveness of elementary school traffic calming interventions

This is the authors' abstract. We don't add key points for this paper.

Background Collisions with motor-vehicles are a leading cause of severe child bicyclist and pedestrian injuries in Canada. Injury rates and severity are associated with traffic speeds and volume but are moderated through traffic calming. Objective To assess the association of specific traffic calming measures on changes in traffic speed and volume, and active transportation prevalence, around Calgary, Alberta, Canada elementary schools, both immediately following installation and months later. Methods A uniquely modified stepped wedge randomized controlled trial was conducted at a sample of 52 public elementary schools, from July 2020 to May 2021. Outcomes included traffic speed, traffic volume, and active transportation counts. Data were collected pre- and post-installation for all schools, and up to 32 weeks post-installation at select schools. Results In-street signs were associated with a reduction of between 0.53 and 0.94 km/h (on average) in traffic speeds, depending on time-period. Traffic calming curbs were associated with a reduction of 0.80 km/h during the morning time-period. In-street signs were associated with a reduction of active transportation prevalence in the morning, and an increase in the afternoon. Conclusions Small reductions in traffic speed and volume were observed at locations with in-street signs, with potential reductions to child active transportation injury risk. The use of a modified stepped wedge trial design to evaluate traffic calming features is unique and may guide further evaluation of built environment effects on health outcomes. Studies should assess whether expanding to roadways with higher speed limits may lead to greater reductions in speed.