Air quality

The RTA is committed to safely monitoring and managing air quality within Sydney’s tunnels, as well as within surrounding communities. Motorway tunnels take cars off local streets, improving surface air quality. Inside the tunnels, sophisticated measurement and ventilation systems ensure that air quality meets strict regulations governing emissions levels.

How the RTA manages air quality

Air quality in Sydney’s motorway tunnels is managed by flushing the tunnel with fresh air.
This dilutes the pollutants emitted from vehicles as they travel through the tunnel. Mixing large volumes of fresh air with the vehicle emissions ensures that the concentration of pollutants remain within set limits.
Fresh air is drawn into the tunnel portals by fans which also move the air along the tunnel at high speed.  In some tunnels additional fresh air is drawn into the tunnel using large fans at an air intake point.

Once air has travelled along the tunnel it is expelled via an ventilation stack. Typically, a ventilation stack contains large axial fans  which blow the tunnel air out at high speeds. 

Exhaust is well dispersed. This prevents  pollutants from accumulating at ground locations around the stack.

Measuring pollutant levels in the tunnel 

Monitors in the tunnel measure pollutant levels along the length of the tunnel. Air quality is also measured in the stack and at ground locations around the stack.

Sydney’s tunnels are operated in accordance with the conditions of approval set by the Minister for Planning for each project and include strict air quality goals for both inside and outside the tunnels.
 

Air quality and the Cross City Tunnel

Motorway tunnels improve air quality by taking cars and their emissions off surface streets. Better air quality in Central Sydney was one of the key objectives of the Cross City Tunnel. Studies show air quality is significantly improved, with up to 40,000 vehicles a day travelling in the tunnel instead of using existing streets.

Air is released from the tunnel via 9 single 63-metre high ventilation stack located west of Harbour Street, between the existing Harris Street and Market Street viaducts above the eastern side of Darling Harbour.

The tunnel has been designed to reduce the need for emissions at the tunnel portals (entrances and exits) and provide better air quality in the tunnel during an incident such as a traffic accident or vehicle breakdown.

In normal operating conditions, air travels east in the eastbound tunnel before being directed into the westbound tunnel to travel to the ventilation stack. A ventilation tunnel has been constructed beneath the road tunnels for use during congested conditions and other incidents. At these times, air from the eastbound tunnel will be transferred into the ventilation tunnel to the ventilation stack. This will mean portal emissions may only be required in extreme circumstances.

Checking air quality

Comprehensive air quality in-tunnel monitoring is being undertaken. Real-time air quality information from  in-tunnel monitors, as well as relevant meteorological data such as wind factors, are available on www.crosscity.com.au.