Invention of a new device to optimise air quality for vehicle occupants in Sydney’s tunnels: the Car Canary

Traffic-related air pollutants (TRAP) present a risk to vehicle occupants (VO) when driving in tunnels. Recirculating vehicle cabin air (RVCA) is the current recommended strategy to protect motorists from TRAP exposure. TRAP and carbon dioxide (CO2) concentrations were hypothesised to be higher in tunnels, with RVCA reducing TRAP but increasing exposure to CO2. Air quality testing in tunnels confirmed the presence of TRAP and that CO2 accumulates in a passenger vehicle when two VO use RVCA. The measured levels of CO2 indicate poor ventilation and a build up of re-breathed air, which may increase the risk of transmission of airborne viruses when an infectious person is present, along with fatigue or drowsiness that may be relevant to driving behaviour. Three scenarios were tested using different combinations of RVCA and window use. Testing indicated a trade-off: particulate matter 2.5 μm or less in diameter (PM2.5) exposure was highest with windows open and lowest with windows closed and RVCA enabled, while CO2 exposure was highest when RVCA was enabled. Driving with windows closed and RVCA disabled reduced CO2 exposure but slightly increased PM2.5 exposure. To help manage this tradeoff, a prototype device known as the Car Canary was developed to alert VO when PM2.5 reaches a set point, indicating when to enable RVCA. These preliminary findings from the WestConnex M4–M8 tunnel system suggest that closing windows while using the device to guide RVCA use may help balance exposure to CO2 and TRAP, although further research is needed. This proof-of-concept device, known as Car Canary was invented and successfully tested in this pilot study.