This paper shows the results of work carried out to study accidents in Spanish road tunnels. The research focuses on tunnels longer than 500 m. It covers 449 accidents in 184 tubes and 230 more accidents close to their portals, all of them with casualties, during a 10-year period. This work analyses several relevant characteristics of traffic accidents in road tunnels, such as their frequency (comparing accident rates in tunnels and on the open road), type and cause. It also estimates the correlation with accident rates involving other characteristics of tunnels, such as circulation (unidirectional as opposed to bidirectional tunnels), length, traffic, longitudinal slope and location. Among other conclusions summarised in this paper, the study shows that tunnels have an accident-reducing effect compared to open stretches of road. This effect increases with tunnel length and it has a major impact for roads with higher accident rates, such as single-carriageway roads.
