The threshold effects of bus micro-environmental exposures on passengers’ momentary mood

The bus plays a crucial role in the daily travel of urban residents. Previous research on bus micro-environmental exposures and their adverse impacts on passengers’ health and comfort has attracted considerable attention. However, few studies to date have explored the correlation between bus micro-environmental exposures and passengers’ momentary mood, examined the thresholds of various micro-environmental factors, and analyzed the optimal micro-environmental exposure levels for passengers. To this end, both micro-environmental exposures and questionnaire survey data are simultaneously collected from 543 passengers in randomly selected buses operating on the 6 routes in Guangzhou, China. Multiple regression models are then applied to explore some research gaps in the existing literature. The results suggest that in-bus noise and passenger load have negative overall correlations with passengers’ momentary mood, whereas temperature and relative humidity have positive overall correlations with it. Passengers’ momentary mood is subject to the threshold effects of these four micro-environmental indicators. The thresholds of in-bus noise, temperature, and relative humidity identified in this study are 65–79 dB, 30–34 °C, and 50–65% respectively. In terms of passenger load, 8–18 is a threshold below which momentary mood gets worse, and 19–29 is the other threshold beyond which momentary mood deteriorates considerably. Further, the optimal exposure levels of these bus micro-environmental indicators are 0–65 dB, 22–28 °C, 41–50%, and 18–19 respectively. These threshold effects provide valuable implications for transportation planners and bus operators to achieve desirable and user-friendly in-bus micro-environment based on a better understanding of the changes in passengers’ momentary mood.