Traffic safety is a key success factor for road tunnel safety. In general, on a yearly basis, most injuries and fatalities in tunnels are related to traffic incidents that could also happen on the open road. However, since a tunnel is an enclosed space, the escalation of a collision, in terms of fire and the release of dangerous goods, could have far more serious consequences than on the open road, because more people than those directly involved in the incident can potentially be exposed to the hazards of heat, smoke, explosions or toxic gases. Moreover, the tunnel itself can contribute to the cause or the effects of a collision, for instance because of changing light conditions (the “black hole effect” when entering the tunnel) or because the tunnel wall is an “unforgiving obstacle” that can worsen the mechanical impact of a collision or impede a successful evasive manoeuvre.
Compared to the open road, there are several factors that may influence the probability or the effect of a collision in (and nearby) tunnels in a positive or negative way:
All in all, the tunnel manager must consider traffic safety in a specific tunnel in terms of risks and measures; he must analyse and evaluate the risks (on the basis of criteria for both traffic safety and tunnel safety) and he must consider, choose and implement measures to control these risks. For new to be built tunnels, this has already to be taken into account in the planning and design phase. For existing tunnels, the tunnel manager has to evaluate the safety situation in practice (feedback from experience, learning from actual incidents or near-incidents) and take measures to improve the situation when necessary.
Of course, not all the causes, like drunk driving, mobile phone use while driving, or the defective technical condition of a vehicle, are within the circle of influence of the tunnel manager. The same goes for the effects of the collisions. However, the tunnel related causes and effects can be effective targets for the measures to reduce the risk of collisions.
More qualitative and quantitative information that is useful for the risk assessment of collisions in road tunnels can be found in the report 2016/R35 “Experience with significant incidents in road tunnels”, notably in chapter 3. In the cycle 2016-2019, WG2 (Safety) of TC D.5 (Road Tunnel Operations) is drawing up a report “Prevention and mitigation of tunnel related collisions” on the (cost) effectiveness of the various measures that are at the disposal of the tunnel manager to control the collision risks.
Other useful reports on the subject include: