Risk factors of road traffic injuries among motorcyclists in Dar es Salaam, Tanzania

Abstract: Background: Commercial motorcycling has become an alternative mode of transport and employment in low and middle-income countries, contributing to road traffic injuries and deaths. Still, there is limited context-specific knowledge regarding risk factors associated with commercial motorcycling. Thus, there is a need to deepen the understanding of factors associated with road traffic injuries among commercial motorcycle drivers to provide evidence-based data that can be used to support preventive strategies for road traffic injuries in Tanzania. Aim: The overall aim of the thesis was to identify risk factors associated with motorcycle-related injuries in the context of the road environment, human behaviour, and work-related factors among motorcyclists in Dar es Salaam, Tanzania. Methods: The thesis is based on four studies with different study designs. Article I is a cross-sectional and observational study using motorcycle-related crash data extracted from the Tanzanian police force. Multiple correspondences and hierarchical cluster analysis were used to assess the profile of high-risk locations for motorcycle crashes. Articles II and III are based on a population-based case-control study of commercial motorcycle drivers. Article II was used to assess the effect of alcohol consumption and marijuana use on the risk of road traffic injuries. The cases were commercial motorcycle drivers who sustained road traffic injuries leading to hospital attendance, while controls were drivers recruited from the parking stage from the same source population as the case and who had not experienced any road traffic injuries leading to hospital attendance in the past six months. Logistic regression models were used to estimate the associations. Article III was performed to determine the effect of motorcycle ownership on the risk of road traffic injuries and the mediating roles of risky driving behaviour and the number of working hours. The associations were estimated using binary logistic regression and decomposition analysis. Assess the mediating roles of risky driving behaviour and the number of working hours. In Article IV, a cross-sectional study was performed to study the association between financial stress and risky driving behaviour and to assess if types of motorcycle ownership moderate that relationship. Modified Poisson regression with the robust error was used to estimate the prevalence ratio. Results: Article I: We identified three clusters of hot spots of motorcycle crashes with different levels of injury severity differing according to road infrastructure and traffic density attributes. High-risk locations for fatal motorcycle crashes were overrepresented with areas located on trunk roads, with a mixture of different types of road users, and where trunk or collector roads ran through residential and commercial areas. Article II: Risky drinking was associated with 2.41 times higher odds (95% CI: 1.01 - 5.76) of road traffic injuries among commercial motorcycle drivers. Article III: Regarding occupational exposure, the odds of road traffic injuries were significantly higher among drivers who co-owned their motorcycles (OR=3.65, 95% CI: 2.12 - 6.28) and renters (OR=2.25, 95% CI: 1.36 - 3.75). Mediation analyses showed that risky driving behaviour and the number of working hours partially mediated the associations between types of motorcycle ownership and the risk of road traffic injuries. Article IV: Financial stress was associated with 3.27 times higher (95% CI: 2.07 - 5.17) prevalence ratio of risky driving behaviour. Risky driving behaviours were significantly higher among co-owners (PR=2.43, 95% CI: 1.48 - 4.00) and renters (PR =2.33, 95% CI: =1.43 - 3.80) compared to self-owners. There was a significant interaction effect of high financial stress on risky driving behaviours with co-owners (PR=0.46, 95% CI: 0.23 - 0.77) and renters (PR=0.44, 95%CI: 0.26 - 0.76). Conclusion: Clusters of hotspots of motorcycle-related injuries were characterized by unseparated two ways, trunk roads, at T-junctions, in residential and commercial areas with a mixture of different road users. Risky alcohol use was associated with increased odds of road traffic injuries among commercial motorcycle drivers. The findings showed that co-owning or renting a motorcycle exacerbates the odds of road traffic injuries. Further, financial stress was associated with increased odds of risky driving behaviour. Co-ownership or rental modifies the association between financial stress and risky driving behaviour. These findings underscore the need to consider human and work-related factors when implementing preventive measures for road traffic injuries involving motorcycles.