Spatio-temporal analysis of road traffic crashes by severity

• Crash severity and collision types show distinct patterns across the city center to the periphery of urban structure. • Urban centers exhibit a higher proportion of minor injuries, while peripheral areas had more fatal and serious crashes. • Nighttime is a critical period for fatal crashes, peaking in the late evening in inner and intermediate zones and during daytime in outer zones. • Vehicle-pedestrian collisions posed the highest risk, revealing unique spatial patterns across the urban landscape. Understanding road traffic crashes' spatial and temporal dynamics is essential for targeted safety interventions. Prior studies often rely on spatial units like junctions, road segments, traffic analysis zones, or broad urban-rural classifications. However, this dichotomy limits insights into crash patterns along the urban-periphery continuum. This study analyzes three years of georeferenced crash data from Addis Ababa using equally spaced radial zones from the crash center as spatial units. A combination of descriptive statistics, nonmetric multidimensional scaling, and multinomial logistic regression was employed to investigate spatial and temporal crash patterns, while the Knox test was applied to identify statistically significant spatio-temporal clustering. Results indicate minor injury crashes are more frequent in inner-city, whereas fatal and serious crashes dominate peripheral zones. Nighttime crashes, particularly in late evening hours, are more lethal in inner and intermediate zones, while fatal crashes in peripheral areas primarily occur during the daytime. Vehicle-pedestrian collisions pose the highest risk, followed by rear-end, sideswipe, and head-on crashes. Fatal and serious crashes are significantly more likely on weekends and at night, with severity increasing with distance from the city center. The Knox test confirms strong spatiotemporal clustering of fatal crashes within a two-week window and 100m-150 m range at 99.9 % confidence. For spatial ranges of 200m-300 m, clusters persist for 59–71 days. Clusters at 500m-1250 m thresholds emerge within 13–27 days, with 1000m-1250 m ranges exhibiting similar patterns. The findings highlight the limitations of the urbanrural dichotomy and emphasize alternative zoning methods for improved spatial and temporal analysis in road safety.