Safety Optimised in the Raimeux Tunnel in Switzerland
The 4.3 km Choindez-Moutier North cross-cantonal section on the trans-Jura highway A16 in Switzerland opened to traffic on 30th November, 2007. It comprises the 220 m Roche St-Jean tunnel and the 3,220 m Raimeux tunnel, which consists of a main, bidirectional tunnel with one lane in each direction, and its parallel safety bore. Read E-News Weekly 1/2008. Since safety in long bidirectional tunnels is a crucial issue since the disastrous Alpine tunnel fires in 1999-2001, the tunnel has been equipped with the most complete and modern devices to meet the highest health and safety standards.
Operation and safety
The substantial technical devices installed in the Raimeux tunnel for its good safety and operation are aimed at achieving an optimal management of any potential incident or accident in what is the longest tunnel on the A16 in the canton of Bern.
The goal of the ventilation system is to remove the vitiated air in normal conditions and fumes in case of fire. Numerous measuring points permanently check the traffic within the main tunnel by measuring the air speed, opacity and carbon monoxide concentration. The temperature and the humidity in the main tunnel are also measured. A temperature control system allows to detect fires. A video monitoring system of 42 cameras looks at the entire tunnel and supplies the automatic detection of incidents. An FM radio signal is broadcasted in the tunnel to inform roads users in case of problem. This is the reason why it is recommended to drivers to tune their radio on the FM station indicated at the tunnel entrances when they drive through a tunnel on the Swiss national roads. In the Raimeux tunnel, drivers are invited to tune their radio on 88.8 (French-speaking Swiss radio).
All the data collected automatically by the safety instrumentation is recorded in the main control room situated in the middle of the tunnel (see sketch). Only the most important events, such as fire alarms or electric voltage drops, are transmitted in real time to the regional control centre in Biel, that is then responsible for mobilizing the rescuers and to manage the signs (lane closures, traffic deviation, etc.).
Even if there is no such thing as zero risk, the numerous safety systems installed in the A16 tunnels are intended to get as close as possible to the zero risk, a near-zero risk situation.
Ventilation
The Raimeux tunnel ventilation is longitudinal with central station. The contaminated air is expelled by a 258 m-high 5 m-diameter vent shaft situated halfway through the main tunnel. The ventilation station housed in a cavern is equipped with two powerful axial fans that blow the air out of the main tunnel. Six jet fans fastened above the carriageway complete, if needed, the central station. In normal situation, the natural thermal climbing force in the vent shaft allows to pump the vitiated air from the main tunnel without the need to use the fans. The ventilation regime is automatically controlled according to the measured values by the opacity and carbon monoxide sensors. Fifty-seven intake valves are installed every 50 metres in the ventilation slab.
In case of fire, the five intake valves closest to the vehicle on fire open automatically while the main vent at the middle of the tunnel is closed. The two axial fans are switched to full speed to blow the fumes through the five open intake valves and evacuate these fumes through the ventilation duct and then the shaft. In case of fire near the portals, the smoke is evacuated directly through the portal by means of the jet fans. A fan blows fresh air to every end of the parallel safety tunnel so that there is a permanent overpressure within it compared to the main tunnel.
Emergency exits
The new bidirectional tunnels like the Raimeux tunnel have a parallel 3.6 m-wide safety gallery alongside the main tunnel. This gallery is accessible every 300 metres through cross-passages signalled by fluorescent pictogrammes placed each 25 metres on the tunnel walls, by an optical guidance on the roadway edges and by luminous columns on either side of the access doors. The SOS niches are equipped with a fire extinguisher and an emergency call telephone.
Signs and lighting
Several signage panels, installed nearby the entrance of every motorway tunnel, aim at helping road users pay attention to driving in tunnels. These panels generally indicate the tunnel’s name and length, the authorised speed (80 km/h in the Raimeux tunnel) and the overtaking ban. It is recommended to switch on the headlights, to keep a safe distance and to listen to the radio at the mentioned frequency. Progressive and variable intensity luminaries according to the external luminosity enable drivers to adapt to the light differences at the tunnel’s entry and exit.
Video monitoring
One of the most important instruments of the safety equipment is the video monitoring system. Fourty-two cameras, placed every 150 metres, film permanently the traffic in the Raimeux tunnel. The cameras have been installed so that they can watch every corner of the tunnel. They are stationary and without zoom. These two properties make it possible to optimise the automatic incident detection thanks to a video image processing software. Wrong-way driving, a crossing of the double white centre line or a stopped vehicle will be immediately detected and located. Visit www.a16.ch 04/08.
Ventilation chimney of the Raimeux tunnel
