![](https://cdn.theconversation.com/files/178765/width926/file-20170719-13554-1ipv02.jpg)
This week news broke about the location of several exhaust ventilation stacks that will disperse vehicle pollution along some of the 14 kilometres of tunnels planned across Sydney.
Four of the six 20-35 metre tall exhaust stacks would be near schools, with the private girls’ school Wenona, Anzac Park Primary School in Cammeray and Seaforth Public School each being within 200 metres.
ABC TV’s 7pm Sydney news bulletin on Monday July 17 told viewers the stacks in the North Sydney area would be:
near dozens of schools, pre-schools and parks … When the Lane Cove tunnel was built the unfiltered stacks were placed in the nearby industrial area. Residents want these stacks built in the Artarmon industrial estate and filtered.
Eleven schools were named in the online report.
Does the evidence stack up?
The Lane Cove tunnel stacks were the focus of a major research project conducted by some of Australia’s most renowned environmental health researchers in air quality and respiratory health.
They recruited 2,978 residents in the year before the tunnel opened (2006) and in each of two years afterwards (2007–2008).
These residents lived in one of four exposure zones, including a control zone. The residents completed a questionnaire about their respiratory symptoms in each of the three years. A sub-group of 380 people also had their lung function tested using spirometry, which measures how well someone can move air into and out of their lungs, and their ability to breathe out air (peak expiratory flow). This sub-group also recorded any symptoms twice a day for nine weeks.
Despite a major reduction in traffic from 90,000 to 45,000 vehicles a day along the main road the tunnel bypassed, there was no consistent evidence that the respiratory health of people living along that road had improved.
However, people who lived near roads feeding into the tunnel reported more upper respiratory symptoms in the survey group but not in the panel sub-group. Those living within a radius of 650 metres of the tunnel ventilation stack also reported more upper and lower respiratory symptoms and had lower spirometric volumes (reflecting poorer lung health) after the tunnel opened. Although importantly, air pollutant levels near the stack did not increase over the study period.
Unexpected results
The authors said some of these results were “unexpected” because another similar study of an exhaust stack on Sydney’s M5 had shown no differences between before and after the exhaust started operation.
Their report discussed a number of methodological reasons to explain the Lane Cove findings (see the detailed discussion section here).