Objective To advance the interpretation of the ‘safety in numbers’ effect by addressing the following three questions. How should the safety of pedestrians be measured, as the safety of individual pedestrians or as the overall safety of road facilities for pedestrians? Would intersections with large numbers of pedestrians exhibit a favourable safety performance? Would encouraging people to walk be a sound safety countermeasure?
Methods We selected 288 signalised intersections with 1003 pedestrian crashes in Hong Kong from 2010 to 2012. We developed a Bayesian Poisson-lognormal model to calculate two common indicators related to pedestrian safety: the expected crash rate per million crossing pedestrians and the expected excess crash frequency. The ranking results of these two indicators for the selected intersections were compared.
Results We confirmed a significant positive association between pedestrian volumes and pedestrian crashes, with an estimated coefficient of 0.21. Although people who crossed at intersections with higher pedestrian volumes experienced a relatively lower crash risk, these intersections may still have substantial potential for crash reduction.
Conclusions Conclusions on the safety in numbers effect based on a cross-sectional analysis should be reached with great caution. The safety of individual pedestrians can be measured based on the crash risk, whereas the safety of road facilities for pedestrians should be determined by the environmental hazards of walking. Intersections prevalent of pedestrians do not always exhibit favourable safety performance. Relative to increasing the number of pedestrians, safety strategies should focus on reducing environmental hazards and removing barriers to walking.
- statistical issues
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Contributors PX and SCW identified the research gap. SX and PX collected the data. PX analysed the data, designed the model, drafted the manuscript and made the revision for submission. SCW, ND and HH provided comments on earlier drafts and made editing corrections. All of the authors have read and approved the manuscript.
Funding This work was jointly supported by the Joint Research Scheme of National Natural Science Foundation of China/Research Grants Council of Hong Kong (Project Nos. 71561167001 and N_HKU707/15). SCW was also supported by the Francis S Y Bong Professorship in Engineering.
Competing interests None declared.
Ethics approval Human Research Ethics Committee for Non-Clinical Faculties, The University of Hong Kong.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement The data sets are owned and were made accessible to the authors by the Hong Kong SAR Government.