The complex interrelation of walking and thermal stress: surprising results from large-scale pedestrian monitoring of a main street using machine vision

The challenge of increasing walking in cities has attracted considerable attention among urban planners and designers in recent years, focusing mainly on enhancing street connectivity, walking strip safety and continuity, and the short-distance concentration of urban amenities. Interestingly, little attention has been given to the relation between urban design, climatic conditions, and walking. While we assume that an increase in outdoor heat stress would result in a decrease in people’s willingness to walk, empirical evidence on the actual behaviour of pedestrians in response to such conditions is rare. 

This study examines the assumption that pedestrian traffic would probably decrease as thermal stress increases by analysing a large-scale pedestrian count dataset. The dataset was created using machine vision analysis of video streams from two cameras overlooking a poorly shaded main street in Tel Aviv-Yafo. The high temporal resolution (15 months of continuous monitoring) and the high number of counted pedestrians (about 2.5 million) allowed for characterising the street’s “circadian rhythms” for different times of the week and the year while examining if and how the changing climatic conditions affect the nature of these trends and their magnitude. 

Contrary to our hypothesis, the counts revealed that weekday pedestrian traffic increased in the hot season during the daytime and nighttime alike despite the excess and sometimes extreme heat stress pedestrians were exposed to. The data also showed consistent differences in pedestrian flow between weekdays and weekends, with the most profound seasonal difference manifested on weekdays. These findings indicate that urban walking patterns, at least on main streets, may be highly dependent on routine outdoor activity patterns that may have more impact on walking choices than the preference to avoid exposure to severe heat stress. They also highlight the need to further study pedestrian behavioural patterns and their relation to urban microclimatic conditions.