A tunnel study to validate motor vehicle emission prediction software in Australia

- Tunnel studies are useful to partially validate vehicle emissions software.
- Air flow in tunnels can compensate the impacts of road gradients on vehicle emissions.
- Local fleet mix is an essential factor in validation studies.

A tunnel emissions study was conducted to (partially) validate the Australian vehicle emissions software COPERT Australia and PIARC emission factors. The in-tunnel fleet mix differs substantially from the average on-road fleet, leading to lower emissions by a factor of about 2. Simulation with the PΔP software found that in-tunnel air-flow compensates to a large extent for road gradient impacts on NOx emissions. PIARC emission factors are conservative and exhibit the largest prediction errors, except for one very good agreement for LDV NOx. COPERT Australia is generally accurate at fleet level for CO, NOx, PM2.5 and PM10, when compared with other international studies, and consistently underestimates emissions by 7%-37%, depending on the pollutant. Possible contributing factors are under-representation of high/excessive emitting vehicles, inaccurate mileage correction factors, and lack of empirical emissions data for Australian diesel cars. The study results demonstrate a large uncertainty in speciated VOC and PAH emission factors.

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