Because a road tunnel is an enclosed space, many tunnel safety measures are rightfully aimed at controlling the risks of fires and dangerous goods. However, practice generally shows that most injuries and fatalities in tunnels are actually related to traffic incidents that could also happen on the open road. This means that measures to assure traffic safety are also very important.

Usually, several causes contribute to a specific collision occurring in a tunnel, or in its direct vicinity. Not all these causes, for instance drunk driving or the use of a mobile phone while driving, are within the circle of influence of the tunnel manager. However, to ensure the required level of safety of the tunnel, or to improve safety when needed it is essential for the tunnel manager (and other stakeholders) to have an overview of the possible measures to control the risk of collisions.

To support this need, this report presents and recommends possible organizational and technical measures one can implement to lower the probability (prevention) or the mechanical consequences (mitigation) of tunnel related collisions, that is, collisions in which the specific characteristics of a tunnel play a role in either the cause or the effect.

The presented measures were derived from literature, experience of the Working Group members and an international survey of case studies of actual tunnel-related collisions. This survey was performed through interviews with tunnel operators and other experts in various countries.

As a basis for the survey, a categorization of tunnel-related collision types was defined.

The possible measures were also categorized, each category reflecting the function of the measure, related to possible causes or effects of a collision. Next, the measures in each category were evaluated against the following criteria:

• Effectiveness to reduce a (specific) collision risk;
• Possible effects (positive, neutral or negative) on other aspects that are important for tunnel safety, like the possibilities for self-evacuation in case of fire and emergency response;
• Complexity of the implementation;
• Life cycle costs;
• Resulting cost-effectiveness (based on the above-mentioned criteria).

It appears that there are many measures that are potentially cost-effective to either reduce collision risks in general or to reduce the risks of a specific collision type.

The report is completed with conclusions, recommendations, a bibliography and glossary and several appendices, containing back ground information and details on the measures.