Street vitality and traffic risk: a multiscale analysis of Barcelona and Warsaw

• Street vitality from POI density and streetscape safety, is positively associated with crash risk at the city scale. • Within hotspots (5–16% of segments), functional density fades, but streetscape safety still predicts higher crash counts. • Street length and traffic volume predict crashes in both the citywide and hotspot models. • Vitality-related crash risk is stronger in Barcelona than in Warsaw, implying that urban form shapes collision likelihood. This study examines the relationship between street vitality and traffic crash risk in Barcelona and Warsaw using street-level spatial regression models and group-based temporal clustering. Street vitality, operationalised as functional density and computer-vision-derived streetscape safety scores, shows a positive association with crash frequency across the street network in both cities, supporting the hypothesis that lively streets increase exposure and possibilities for conflict. However, street vitality explains only part of this risk dynamic: street length remains the strongest predictor overall, while building density produces mixed effects. In hotspot models, street vitality effects weaken substantially; functional density becomes insignificant, and visual safety effects diminish, suggesting that once crash concentrations form, risk is shaped more by localised design and behavioural factors than by land-use intensity. These findings underscore the importance of combining system-wide and site-specific perspectives in street safety planning, highlighting the need for design interventions that reconcile lively public spaces with traffic safety.