A complex network of systems and instrumentation needs to work together to deliver safer tunnels. This includes lighting and traffic controls, as well as ventilation, communication, fire protection, and automatic incident detection (AID) systems.
Traffic incidents in tunnels are known to be more dangerous than on a highway. The risk of injury or fatality from a vehicle accident is four times higher in freeway tunnels compared to open roads (Ma et al., 2009). To address the specific risks associated with road tunnel accidents, the EU set minimum safety standards for road tunnels (Directive 2004/54/EC).
Tunnel portal safety challenges
Research shows that the highest collision rates are found in the tunnel portal area, followed by the entrance area, whereas the interior zone shows a significantly lower collision rate (Safety of Road Tunnels, Austrian Road Safety Board). In the research the ‘portal area’ is defined as 10m before/after the portal, and the ‘entrance area’ as 10m to 150m inside the tunnel. Given that video and light-based technologies traditionally used to monitor tunnel traffic can struggle with the variable light and weather conditions at portals, where accidents are most likely, what can be done to improve safety for drivers?
Technology overview
Tunnel operators often use a photometer to measure the luminance, or perceived brightness, of a tunnel portal and its surroundings. This information is used to adjust the tunnel lighting to avoid ‘black hole syndrome,’ which can occur when drivers’ eyes struggle to adapt to sudden changes in light. While this helps maintain driver visibility and can be complemented by other measures, it does not resolve the issue of reliably detecting traffic incidents within these accident-prone areas. Bright light, glare, darkness, as well as fog, rain, and snow are commonly experienced at tunnel portals and can affect the performance of video and light-based monitoring technologies.
Navtech’s radar-based AID technology has been used to improve safety in key strategic tunnels such as the Ryfylketunnelen in Stavanger, Norway, where 102 radar monitor the entire 14.4km (9 mile) twin-bore tunnel.
More recently the technology has been chosen for the Stockholm bypass project due to open in 2030. Selected by Yunex Traffic BV, the 360° radar solution will provide AID coverage at the entrance and exit portals of the tunnels, where extreme changes in light affect vision-based instrumentation and driver visibility.
Radar technology addresses the limitations of traditional video systems by using ‘active’ radio waves to detect objects and incidents in real-time, regardless of lighting conditions. In comparison, ‘passive’ video or light-based technologies rely on the light in the environment for object and incident detection. Networked, long-range 360-degree radar enables full coverage from one end of the tunnel to the other, including at the critical portal areas and extending out on to the road.
Complementary technologies
While radar technology excels at detection in all conditions, video cameras are essential for providing visual context of incidents. Integrating these technologies has the potential to improve the safety of new and existing tunnels. Navtech’s radar-based AID system can direct PTZ cameras to the exact location of an incident, allowing operators to quickly assess the situation visually. This integration creates a comprehensive incident detection and response system, combining the strengths of both technologies for optimal tunnel safety.
Tunnels are a critical feature of any road network, helping to reduce journey times and connect communities. Ultimately, reaching the highest levels of safety for drivers will require using a variety of sensors where they perform best, to raise the overall level of safety.
