Quantitative Risk Assessment Modelling for Non-homogeneous Urban Road Tunnels

Urban road tunnels provide an increasingly cost-ef fective engineering solution, especially in compact cities like Singapore. For some urban road tunnels, tunnel characteristics such as tunnel configurations, geometries, provisions of tunnel Electrical & Mechanical systems, traffic volumes, etc. may vary from one section to another. These urban road tunnels which have characterized non-uniform parameters are referred to as non-homogeneous urban road tunnels. In this study, a novel quantitative risk assessment (QRA) model is proposed for non-homogeneous urban road tunnels because the existing QRA models for road tunnels are inapplicable to assess the risks in these road tunnels. This model uses a tunnel segmentation principle whereby a non-homogeneous urban road tunnel is divided into various homogenous sections. Individual risk for road tunnel sections as well as the integrated risk indices for the entire road tunnel is defined. The paper then proceeds to develop a new QRA model for each of the homogeneous sections. Compared to the existing QRA models for road tunnels, this section-based model incorporates one additional top event: toxic gases due to traffic congestion and employs the Poisson regression method to estimate the vehicle accident frequencies of tunnel sections. This