TUNNEL ENGINEERING

generator sufficient for minimum requirements
should be installed.
Carbon Monoxide Analyzers n These take
continuous air samples from the tunnel and
analyze them for CO content. The results are
visually indicated and also recorded on paper tape,
with time gradations. The recorders are mounted
on the face of the control board, to guide the
operator in selection of number of fans and speed
necessary.
In a longitudinal or semitransverse supply
system, air samples are taken from the tunnel
proper at points of maximum concentration.
In transverse systems, the samples may be taken
from the exhaust ducts.
Haze Control n To measure visibility in
tunnels affected by haze from exhaust gases,
instruments have been developed that give a
reliable indication without excessive maintenance.
Equipment manufactured for the Port Authority of
New York and New Jersey uses the scattering of
ultraviolet light by dust particles. Instruments
protect the optics by recessing them in tubes
through which filtered air is exhausted. Another
type of instrument compares the intensities of two
branches of a split light beam passing through the
same optics, one going through a tube filled with
clean air, the other through tunnel air.
Ventilation Power Requirements n The
power requirements and pressure losses are best
evaluated using the prodedures contained in the
Tunnel Engineering Handbook (J.O. Bickel and
T.R. Kuesel, ‘‘Tunnel Engineering Handbook,’’
Kluwer Academic Publishers, New York).
20.7 Tunnel Surveillance
and Control
Emergency exhaust ventilations systems in short
tunnels or tunnels with very light traffic may be
activated by such instruments in the tunnel as
carbon monoxide analyzers or fire-alarm or
telephone boxes connected to the nearest fire and
police departments. Emergency operation for other
types of tunnels should be supervised by personnel
in control centers.
TUNNEL ENGINEERING
Tunnel Engineering n 20.15
Control of many newer tunnels is programmed
for computer operation. The computers, however,
may be bypassed for manual operation in an
emergency.
To permit surveillance of tunnel traffic by
personnel in the control room, monitors may be
installed in that room to display views of the entire
length of the roadways as transmitted by television
cameras mounted in the tunnel. In a short tunnel,
each camera covers a specific stretch of roadway
and transmits to a specific monitor. For a long
tunnel, to limit the number of monitors required to
a convenient number, groups of cameras may be
operated in sequence to transmit to their monitors.
In an emergency, the sequence can be interrupted
to permit a specific camera to focus on the region of
concern.
Traffic Control n Signal lights generally are
mounted at the portals of a tunnel and at intervals
in the interior such that at least one traffic light is
plainly visible within a safe stopping distance. In a
tunnel with two-way traffic, the signals facing
traffic may incorporate red, amber, and green
lights. Lights on the reverse side of those signals
may be red and amber, to permit lane alternation
in an emergency. In a tunnel with two-lane, oneway
traffic, the signals facing traffic carry red,
amber, and green lights, whereas lights on the
reverse side of signals for the left lane may be
amber and red, to permit two-way traffic in an
emergency.
Traffic flow may be monitored by pairs of
electric induction coils that are embedded in the
pavement of each lane and that report the flow on
indicators in the control room. If traffic velocity is
too slow, for instance, less than 5 to 10 mi/h, the
traffic lights are changed to amber, for caution. If
traffic stops, the lights are changed to red. If
necessary, for slow traffic, the traffic lights may be
alternated between stop and go to space traffic flow
into the tunnel.
Fire Control n Automatic fire detectors may be
installed in the ceiling throughout a tunnel. When a
fire occurs, they indicate the location and send an
alarm to an operator who alerts an emergency
crew. If the operator verifies the alarm (which
might have been activated by the heavy exhaust of
a diesel engine rather than by a fire), an emergency
program can be started: The emergency crew and
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