Beyond Crashes: The Silent Burden of Non-Physically Injurious Traffic Externalities in Nigeria- An Integrative Review

Abstract

Urbanisation and rapid motorisation across Nigeria have intensified chronic environmental exposures associated with road transportation systems. While road traffic crashes have historically dominated transport safety discourse, accumulating evidence indicates that non-physically injurious traffic externalities including traffic-related air pollution (TRAP), noise, vibration, and heavy-metal contamination constitute a significant but under-recognised burden on public health and environmental sustainability. These “silent burdens” do not manifest as immediate physical injuries but progressively contribute to respiratory and cardiovascular diseases, cognitive impairment, psychosocial stress, and ecological degradation. This study adopts an integrative review methodology, systematically guided by the PRISMA 2020 Statement framework to enhance transparency and rigour in the identification, screening, and selection of relevant literature. Evidence was synthesised across multidisciplinary domains, including environmental engineering, epidemiology, behavioural science, and urban policy, drawing on peer-reviewed and grey literature published between 2000 and 2025. The PRISMA-guided process resulted in a final corpus of 50 studies, enabling a comprehensive examination of exposure pathways, health outcomes, and contextual drivers. Findings reveal disproportionately high exposure levels among socio-economically marginalised populations residing or working along major traffic corridors, largely driven by weak regulatory enforcement, inadequate urban planning, and pervasive informal land-use practices. The review further identifies critical gaps in environmental monitoring systems, policy integration, and longitudinal health evidence. Thus, the study demonstrates that non-physically injurious traffic externalities represent a major yet systematically neglected public health challenge in Nigeria and similar developing contexts. Addressing these cumulative risks requires a paradigm shift toward integrated policy responses, including strengthened environmental monitoring, enforcement of land-use setbacks, reform of vehicular emission standards, and the mainstreaming of environmental health considerations into transport and urban planning frameworks. This review provides a robust evidence base for advancing policy reform and guiding future research aimed at mitigating the long-term health and environmental impacts of transport-related externalities in rapidly urbanising regions.