There are more losers than winners in the completion of the new NorthConnex Tunnel, but everyone could still be winners.


The construction of the NorthConnex tunnel linking the M1 Pacific Motorway at Wahroonga to the Hills M2 Motorway at West Pennant Hills will result in great benefits to the thousands of drivers of cars and trucks that daily face  traffic congestion traversing Pennant Hills Road. Residents of surrounding suburbs will also gain relief from decreased exposure to heavy vehicles and general traffic.


Motorists and residents will share in common the concentrated air pollution within the tunnel and its distribution to the surrounding areas.

Despite assurances from NorthConnex and Roads & Maritime, the proposed ventilation management system will not deliver clean, unpolluted air to drivers or residents. The tunnel needs not only a better ventilation system, but a high performance filtration system.

Identifying the problem

Noel Child of engineering and environmental consultancy NG Child & Associates has stated the problem clearly.

“The longitudinal ventilation system slated for installation in the NorthConnex project may not be the best option available, and could result in severe air quality problems for the project,” he said.

 It’s not the first time the best option for tunnel ventilation has not been chosen.

Child advocates the construction of a transverse ventilation system, which he says is far better suited to a long-distance, heavy traffic tunnel, as it involves the delivery of fresh air into the tunnel at multiple points along its distance.

How is NorthConnex planning to deliver in-tunnel air quality?

“The NorthConnex ventilation system will be designed with a longitudinal ventilation system, with air drawn in the entry portals by moving traffic. This is the most commonly used ventilation design around the world,” according to the Air quality and the northern interchange at Wahroonga, NorthConnex fact sheet from June 2014.

That method may be commonly used, but for short tunnels, not for nine-kilometre tunnels.

“At the main portals tunnel air will be extracted through a ventilation outlet to effectively and safely disperse the air into the atmosphere. Jet fans are used to keep fresh air flowing through the tunnel (when traffic is slow or stopped) to ensure the air quality within the tunnel meets the air quality criteria and to minimise haze within the tunnel,” the fact sheet says.

The decision to not use filtration is based on the Roads and Maritime $60million, 18-month trial of in-tunnel air filtration of M5 East tunnel.

This flawed trial focused on the effectiveness of an air filtration technology in removing particulate matter (PM) and nitrogen dioxide (NO2) from the air in the tunnel.

The conclusion was the air quality benefits did not justify the operational and capital costs. However, the tested system generated toxic waste, destined for landfill, and incurred huge maintenance costs. For similar reasons, this system has been abandoned or has restricted use in tunnels across Europe.

NorthConnex claims that “filtration technology is not proposed on the NorthConnex tunnel ventilation system, as it would not deliver any benefits to the surrounding community.”

Part of their solution is to ask “commercial vehicle operators to adopt cleaner technologies” with “fines for smoky vehicles in tunnels.”

The NSW Government Advisory Committee on Tunnel Air Quality says, “there are scientific knowledge gaps regarding the effects of very brief (a few minutes) exposures to high levels of air pollutants on health, and regularly repeated exposures, as occur in road tunnels.”

We wouldn’t drink even slightly polluted water supplied by Sydney Water and yet we are expected to breathe unknown degrees of polluted air (supplied by NorthConnex), both inside and outside the tunnel.

Earth Air Purification as a possible solution

Developed in Japan for cleaning polluted air in tunnels, underground car parks and busy traffic intersections, Earth Air Purification uses plants and soil for bioremediation and phytoremediation, two well-established means of cleaning contaminated industrial waste gases and water. Microorganisms associated with the soil and on the plant roots literally “eat” carbon, in the process cleaning the air, while producing only small amounts of carbon dioxide and water, the same as we exhale in breathing.

Earth Air Purification

Earth Air Purification

The Earth Air Purification system was brought to the attention of the NSW Government and the RTA in a competitive tender process called for filtration of the Lane Cove Tunnel, but was ignored in favour of a ventilation stack.

Earth Air Purification system has been shown to remove more than 80 per cent of nitrous oxide, more than 90 per cent of carbon monoxide, sulfur dioxide and suspended particle matter and more than 75 per cent of non-metan hydrocarbon from the air.

Earth Air Purification installation at entrance to road tunnel Kyoto City

Earth Air Purification installation at entrance to road tunnel Kyoto City

Everyone’s a winner

By incorporating Earth Air Purification with a transverse ventilation system, traffic exhaust fumes comprising nitrogen oxides, carbon monoxide, sulfur dioxide, suspended particulate matter and volatile organic compounds are progressively purified. Discharged air is contaminant free, to the benefit of the surrounding residents. Operational costs become simple, low maintenance of small, above ground landscaped areas along the length of the tunnel with no toxic residues for disposal.

Underground car park exhaust through Earth Air Purification system Shinagawa-ku Tokyo

Underground car park exhaust through Earth Air Purification system Shinagawa-ku Tokyo