the northern entrance and about 35 metres
from the southern entrance to its deepest
point, 25 metres below sea level.
The tunnel joins the Warringah Freeway
at North Sydney, and the Cahill Expressway
at the entrance to the Domain Tunnel.
It has two lanes in each direction and
carries around 90,000 vehicles per day.
How is air quality managed
in the Sydney Harbour Tunnel?
Air quality in the tunnel is managed
with a ventilation building located in the
northern pylon of the Sydney Harbour Bridge.
In addition to air being expelled via the
ventilation building, air is expelled through
the tunnel portals (tunnel entrances and
exits). Air is circulated through the tunnel
by a combination of vehicle movements and
the use of axial fans. Fresh air can be drawn
into the tunnel via a duct located on the top
or side of each tunnel.
The tunnel ventilation system is managed
to ensure carbon monoxide levels within
the tunnel are kept within approved levels
and that visibility for drivers is maintained
at safe levels.
Air quality monitoring
The tunnel operator carries out routine
testing of the air quality in the tunnel and
in the ventilation building. The air quality
is monitored 24 hours a day to ensure levels
stay within the goals set by the former
Minister for Planning
The tunnel is fitted with carbon
monoxide monitors as well as visibility
and air velocity monitors.
The Sydney Harbour Tunnel
The Sydney Harbour Tunnel was completed
and opened to traffic in August 1992 to
provide a second crossing of Sydney
Harbour and to alleviate congestion on
the Sydney Harbour Bridge.
The tunnel is made up of three sections:
twin 900-metre land tunnels on the north
shore, twin 400-metre land tunnels on
the south shore and a 960-metre immersed
tube. The tunnel falls about 55 metres from