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https://www.nationalacademies.org/trb/events

Development of a Crash Modification Factor for Pedestrian Crashes at Roundabout

Roundabouts have been widely adopted as a safety countermeasure at intersections due to their ability to elimate conflict points, reduce vehicle speeds, and improve operational performance. They are classified by the Federal Highway Administration (FHWA) as a Proven Safety Countermeasure based on strong evidence of reduced serious-injury and fatal vehicle crashes when replacing stop-controlled or signalized intersections. However, while the vehicle safety benefits of roundabouts are well established, the evidence regarding pedestrian safety remains limited. Although roundabouts intuitively offer benefits for pedestrians—such as fewer vehicle-pedestrian conflict points, lower speeds at crossings, improved sight lines, and refuge opportunities in splitter islands—the available scientific data on crash reductions for pedestrians is sparse. The few existing pedestrian crash modification factors (CMFs) are generally rated low in quality, with limited sample sizes, methodological shortcomings, and little attention to design variations such as multilane roundabouts, bypass lanes, or roundabout interchanges. As a result, agencies currently lack high-quality, generalizable CMFs to reliably assess the pedestrian safety performance of roundabouts. This project addresses this critical gap by seeking to develop CMFs to quantify the change in pedestrian crash frequency associated with installing a roundabout at an intersection. The analysis will focus on sites previously controlled by stop signs or traffic signals. An observational Empirical Bayes before–after study design will be employed, as it is the state-of-the-art approach for roadway safety evaluations and appropriately accounts for regression-to-the-mean, crash trends, and changes in traffic volumes. In addition to controlling for traditional roadway infrastructure and traffic volume impacts, the research team will also attempt to incorporate pedestrian exposure through surrogate measures, such as demographic and socioeconomic characteristics, land use diversity, network connectivity, and pedestrian infrastructure, drawing on models and metrics the research team has recently developed for North Carolina Department of Transportation (NCDOT). It is anticipated that the resulting CMFs may be in the form of Crash Modification Functions that provide an estimate of the safety impacts of roundabouts as a function of several design variables, if it is determined that any of these impact pedestrian safety performance at roundabouts. Candidate variables that the research team intends to explore the impact on pedestrian safety as a part of this project include: roundabout radius, approach speed limit, level of pedestrian activity (either direct exposure estimates or exposure surrogates), number of travel lanes, traffic volume, speed limit, functional classification, pedestrian crossing or pedestrian infrastructure at roundabout locations, and presence of pedestrian crossing aids (e.g., Rectangular Rapid Flashing Beacons or Pedestrian Hybrid Beacons) or signage. Anticipated products include a final report documenting the CMF development process, the CMFs themselves, and their interpretation. An implementation plan will also be provided, outlining how the CMFs should be applied, the level of confidence associated with the results, and any data quality limitations. The plan will include recommendations for updating NCDOT policies, guidelines, and training resources to ensure that the findings are effectively integrated into planning and design practices. By providing robust, evidence-based CMFs for pedestrian crashes at roundabouts, this research will enable NCDOT to make more informed decisions about the safety performance of roundabout projects, particularly in pedestrian-rich environments.