This study is directed towards providing quantitative information on the risks to the public and the possible damage to tunnel structures from incidents involving the transport of hazardous substances. Four tunnels were singled out as case studies (The Holmesdale (M25), the Conwy, the New Dartford and the Rotherhithe tunnels). These tunnels were specifically selected to cover the wide range of factors that may influence levels of risk inside a tunnel. Section 2 reviews the UK road traffic in hazardous substances carried in bulk or packages. Section 3 describes the various scenarios involving the transport of such substances which may cause damage to the tunnel or harm to its occupants and section 4 analyses the extent of this damage. Section 5 assesses the consequences of similar events occurring on the open road. Section 6 derives incident frequencies which, when combined with the consequence analyses performed under section 4 and 5, enables the evaluation of societal risks as described in Section 7. Societal risks are determined for the two extremes of free access and total exclusion of all hazardous substances through the four road tunnels selected as case studies. In the event of total exclusion, the risks associated with traffic in these materials using a range of diversion routes are examined. Risk levels for the two extreme cases are discussed in section 8 and compared to other levels of risk that have broadly been regarded as acceptable within society. Section 9 draws together the various conclusions that have been forthcoming from the study and discusses areas where future study would prove beneficial. In appendix 7 a reassessment of the risks relating to alternative surface routes to the Dartford tunnel is presented. This study addresses some of the areas identified in section 9 as benefiting from further work.

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