SAFETY - The Westerschelde Tunnel: Approaching Limits - page 44

taken. Besides, maintenance activities are only carried out in the evenings
and at night, when there is an extremely low traffic flow.
Precautions have also been taken to rule out the chances of head-on colli-
sions on the access roads that have two driving lanes: a central reservation
with a barrier gate or crash barrier separates the two traffic flows.
Aside from the prevention of head-on collisions, the accommodation of the
traffic in two tubes also has another major safety advantage (yet not pro-
active, but preventive): in case of fire, the smoke that is released, can be
blown out of the tunnel in the driving direction by means of the jet fans
present in the tunnel. The cars driving towards the fire can stop, but are not
enveloped in smoke because that is being blown away from them. Stranded
motorists can leave the tunnel safely. The cars on the other side of the fire
drive on and don't experience any hindrance. When the traffic from both
directions is accommodated in a single tunnel tube, such a solution is not
possible and the smoke must be discharged in another way: via a smoke
channel above the roof of the tunnel tube, for example as in the tunnels in
the alps.
Regarding the hazards of fire, applicable in the WesterscheldeTunnel for that
matter, there is a prohibition for the transportation of LPG, extremely toxic
substances, explosives and nuclear transports. These pro-active 'organisa-
tional' precautions also eliminate certain types of accidents.
Preventive link: reducing the chances and consequences
Height detection takes place long before the entrance to the tunnel. When a
vehicle is too high, then this is indicated with a traffic light. Besides, before
the traffic drives into the tunnel - which not only concerns trucks - it can be
brought to a standstill by means of barrier gates. Trucks and vehicles with
trailers are prohibited to overtake in the tunnel. Only passenger vehicles
without trailers may make use of both driving lanes in the tunnel.
In the transition zone at the entrance, the cladding of the tunnel walls is
carried out in a reflective material to gently facilitate the transition from light
to dark. The level of lighting in the tunnel can be adjusted automatically or
manually. The entrance lighting is a counter beam light which takes care of
a gradual transition of the level of light from outside to the level of light
inside. Besides, the slanted ingress of light - contra to the driving direction -
results in good visibility (contrast) of the traffic ahead. Automatic detection
systems continually supply information about the CO content as well as the
visibility in the tunnel tubes. The tunnel is provided with a reversible longi-
tudinal ventilation in order to ventilate the tunnel artificially, in case the
maximum allowable air pollution is exceeded in the tunnel, and to dispel
smoke and gases in cases of disaster.
The tunnel is continually monitored from a control building with a closed-
circuit video system. Intercom (which is present in the main tunnel tubes as
well as the cross connections), loud speakers, telephone connections, high fre-
quency radio communication systems (HF) and a normal radio reception of FM
transmitting stations ensure that communication is always possible with the
outside world. Besides, GSM communication is also possible in the tunnel.
The power supply for all the equipment present in the tunnel is provided
by two independent plants on either side of the Westerschelde. In the event
of a power failure on the one bank, at least half of all the systems remain
functioning normally anyway. If the plants on both banks fail simultan-
eously, then a temporary power plant (by means of batteries) provides power
to the most crucial sections of the tunnel. This ensures that a minimum
amount of lighting and control of the tunnel is guaranteed during the period
that is required - if the situation so requires - to clear the tunnel of traffic.