Variable speed limit (VSL) systems are increasingly deployed as part of active traffic management, yet their safety impacts remain heterogeneous and context dependent. This paper presents a structured review of empirical and modeling studies evaluating the safety effects of VSL, with explicit distinction between crash-based and non-crash-based evidence. This systematic review used PRISMA-guided procedures to identify and synthesize 51 eligible studies that span a wide range of methodological approaches, from traditional before–after crash evaluations and simulation-based analyses to more recent data-driven and reinforcement learning–based VSL control frameworks. Crash-based evaluations generally report meaningful safety gains, with VSL associated with reductions in total crashes and in specific crash types, particularly rear-end, weather-related, and injury crashes, with the magnitude of these reductions varying depending on roadway, traffic, and environmental conditions. Complementary non-crash-based evidence shows that these reductions are plausibly mediated by lower speed variance, smoother traffic flow, and mitigation of congestion-induced shockwaves, although many studies rely on assumed compliance and are limited to simulated environments. At the same time, several evaluations highlight that poorly chosen activation conditions, aggressive speed steps, and low driver compliance can erode or even reverse safety benefits. Drawing on this mixed evidence base, the review synthesized practice-oriented guidance on where, when, and how VSL should be implemented. The findings indicate that VSL is most effective on corridors with recurrent congestion, adverse weather, or geometric bottlenecks that produce unstable traffic conditions, and that incremental, harmonization-oriented control strategies with short update intervals are preferable to large step-down speed reductions. The paper proposes indicative decision thresholds for VSL activation based on traffic-flow, weather, and safety triggers, and outlines agency readiness requirements. Overall, the review clarifies the conditions under which VSL is most likely to deliver robust safety benefits and provides a set of evidence-based recommendations to inform design and deployment.
The rapid growth of food delivery cycling worldwide has raised concerns about rider safety in traffic-dense and visually complex urban environments. Many deliveries occur in the evening when visibility is reduced, yet little is known about visibility aid use by delivery bicyclists. This study examined the prevalence and factors influencing visibility aid use among delivery riders. A total of 2900 bicyclists, including 1974 delivery riders, were observed near five busy intersections in Brisbane, Australia during lunch and dinner times. During both day and night, delivery cyclists were consistently more likely than non-delivery riders to use visibility aids: front and rear lights (1.5 times more), fluorescent clothing (2.6 times more), retroreflective clothing (5.3 times more), and retroreflective backpacks (12.8 times more). However, overall usage remained low: only 70.5% of delivery riders used both front and rear bike lights at night despite legal requirements, and few wore retroreflective clothing at night (10.4%) or fluorescent clothing during the day (11.2%). For night-time, a composite visibility score (0–4) was constructed. The most common score was 2 (44.8%), and only 29.1% scored 3 or 4, most frequently by combining mandated lights with retroreflective material (98%). A Generalized Estimating Equations Poisson regression with session-level clustering identified location as the dominant independent predictor of higher visibility scores, while individual characteristics (electric bike use, helmet use, and gender) were not substantive predictors. Visibility practices varied geographically across delivery companies, suggesting that factors beyond environmental conditions may influence visibility behaviour. Organisational-level interventions promoting consistent practices across locations could improve visibility aid use among food delivery riders.
Introduction In a context of demographic ageing and changing mobility practices, understanding how fatality risks evolve once exposure to traffic is considered is essential for designing effective prevention policies. Method This study analyses changes in road fatality risks in France between 2007-2008 and 2018–2019 using police-reported fatal crash data combined with individual travel data from the national mobility surveys. Exposure-based fatality rates are estimated per million person-hours travelled. Analyses are conducted by gender, age group, and type of road user. A decomposition approach is used to disentangle changes in the number of fatalities attributable to variations in exposure from those attributable to changes in fatality rates. Results Over the study period, annual road fatalities decreased by 15%, while total travel time increased by 22%, resulting in a 30% reduction in the overall exposure-based fatality risk. However, trends differed markedly across casualty categories. Young adults (17–29) and the elderly (70+) showed the highest fatality risks per hour travelled. Motorised two-wheeler riders remained the most at-risk despite declining fatality rates. Cyclists experienced a doubling of fatality risk, driven primarily by an increase in fatality rates rather than by greater exposure. Decomposition results show that improvements in fatality rates offset rising exposure for most groups, except for cyclists. Conclusions These findings underscore the need for targeted road safety policies that address both exposure and risk. Improving infrastructure and protective measures for cyclists, alongside adaptations for an ageing population and high-risk motorised users, appears critical to sustain the decline in road deaths.
