Risk Impact Analysis of Traffic Volume and Heavy Goods Vehicles in a Bi-directional Road Tunnel CIRO CALIENDO, MARIA LUISA DE GUGLIELMO Department of Civil Engineering University of Salerno Via Giovanni Paolo II 132, 84084 Fisciano (SA), ITALY ccaliendo@unisa.it, mdeguglielmo@unisa.it Abstract: - A quantitative risk analysis regarding hourly traffic volume (VHP) and percentage of heavy goods vehicles (HGVs) in order to assess their impact on the risk level of a directional road tunnel was carried out. The results in term of social risk, as F/N curves, show that the risk level for certain combinations of VHP and percentage of HGVs is beyond the chosen safety limit (threshold of intolerable risk). As a result, safety measures in order to reduce the risk level must be taken. In this respect, the Tunnel Management Agency (TMA) can permit that HGVs pass through the tunnel only during night or during day along an alternative route that, forming a by-pass for the tunnel investigated, runs completely in open air. The paper also proposes risk charts that are useful for quickly assisting the TMA in making decisions on the most appropriate traffic control strategies. Key-Words: - Quantitative risk analysis, road tunnels, traffic volume, heavy goods vehicles. 1 Introduction Risk analysis is an important tool that can be helpful for improving and/or optimizing the safety level of road tunnels. In this respect, it is to be said that the European Parliament and Council adopted the European Directive 2004/54/EC [1] in which it is clearly required, when a tunnel is opened for example to the transport of dangerous goods, that a risk analysis should be carried out to establish whether additional safety measures and/or supplementary equipment are necessary to ensure a high level of tunnel safety. The Italian Ministry of Infrastructure and Transports [2] has also adopted the aforementioned Directive, and subsequently the Italian Management Agency of National Roads and Motorways (ANAS) has published guidelines [3] for the design of safety in Italian road tunnels. In this regard, a quantitative risk analysis (QRA) is often considered. A quantitative risk analysis is generally based on a probabilistic approach that involves the identification of hazards, the estimations of probability and consequences of each hazard, and the quantification of the risk as the sum of probabilities multiplied by consequences. According to this approach, QRA includes event trees, fault trees and consequences estimation models. Social risk (e.g., the expected number of fatalities in the tunnel per year) is assumed to be the main output of QRA. In particular, social risk is frequently represented in the form of F/N curves, where F is the cumulative probability that the number of fatalities is equal to or greater than a given number N. Different risk models exist in the literature, however in many European countries (e.g. Austria, Switzerland, France, and Greece) the QRAM (Quantitative Risk Assessment Model), which was proposed jointly by PIARC and OECD (Organization for Economic Co-operation and Development) with associated software developed by INERIS [4], is the one most widely used. Applications of QRAM can be found more especially in Saccomanno and Haastrup [5], Knoflacher and Plaffenbichler [6], Hall et al. [7], Parson Brincherhoff Quade & Douglas [8] , Petelin et al. [7], Kyritopouolos et al. [10], Diernhofer et al. [11], Steiger et al. [12], Di Santo et al. [13]. Recently also Caliendo and De Guglielmo [14] have used the aforementioned QRAM for investigating on the impact of dangerous goods vehicles (DGVs) travelling through a bi-directional road tunnel. In particular seasonal variation of traffic, speed of vehicles, and failure of emergency ventilation system were investigated. In this respect, a comparison with heavy goods vehicles (HGVs) was also made. Moreover the risk associated with an alternative route running completely in the open air was also evaluated. However, it is to be stressed that Recent Researches in Mechanical and Transportation Systems ISBN: 978-1-61804-316-0 83