Quantitative Risk Assessment on the Transport of Dangerous Goods Vehicles Through Unidirectional Road Tunnels: An Evaluation of the Risk of Transporting Hydrogen.

A quantitative risk analysis (QRA) concerning dangerous goods vehicles (DGVs), including also vehicles for the transport of liquid hydrogen (LH2TVs), running through unidirectional motorway tunnels was performed. An event tree was built, and a wide parametric analysis based on different geometric and traffic characteristics of tunnels was carried out. The effects of the annual average daily traffic (AADT) per lane, the tunnel length (L), the percentage both of heavy goods vehicles (HGVs) and DGVs (for a given 7% of LH2TVs) were investigated. The results in terms of social risk, as expressed by F/N curves and the expected value (EV), show an increased risk level with the presence of the hydrogen transported, and with certain F/N curves that might also lie above the acceptability limit. This means that additional safety measures should be implemented in order to reduce the risk level or that, alternatively, appropriate strategies of traffic control systems should be taken. A statistical modeling for developing a predictive method of the EV is also performed. The outcomes show that the regression coefficients have the signs expected. In particular, the EV increases with the tunnel length (L), the AADT, and the percentage both of HGVs and DGVs. However, the magnitude of estimated coefficients indicates that the expected value EV increases more with the traffic (AADT per lane, HVGs, or DGVs) than the tunnel length. The application of the approximate method might help the Tunnel Management Agencies (TMAs) in making quick decisions, at a preliminary stage, about temporarily allowing, forbidding or limiting the circulation of DGVs and/or LH2TVs through tunnels; and subsequently investigating in greater depth the potential hazards due to the transport of hydrogen in the worst cases individualized.