The latest data generated by real-world testing of 21 cars sold in Australia have revealed alarmingly high emission numbers, with one of the country's best-selling vehicles one of the worst offenders.
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Fuel consumption again was a big focus of the latest results, but the emission figures generated were equally concerning.
The latest tranche of real-world testing data released under the Australian Automobile Association again revealed how the fuel consumption and emissions produced by car makers' "rolling road" lab tests can be hugely different to those of the real world.
In the tightly controlled lab test, for instance, the little Suzuki Swift five-door hatchback sipped its fuel at very frugal 4.8 litres per 100 kilometres.
But when taken out on the open road under test, the Swift's real world fuel consumption jumped by 31 per cent to 6.3 litres per 100 kilometres.
And in the latest data, two of Mazda's best-selling vehicles over the past five years, the CX-3 crossover and the CX-5 SUV, consumed between 11 and 15 per cent more fuel when exposed to real world conditions.
The $14 million multi-year program by the AAA, which runs road-registered, late-model, randomly selected cars on the same drive route using highly sophisticated measuring equipment, continues to throw up major anomalies in the car makers' claimed fuel consumption.
AAA managing director Michael Bradley said that the aim of the program was to make the federal government's new fuel efficiency standard, which arrives mid-next year, "more robust and more effective" and help to address "greenwashing".
"Real-world testing will drive down demand for [vehicle] models that overpromise and underdeliver," he said.
He warned that consumers should not assume that what is claimed by the car manufacturers, produced in a closed laboratory with specific fuel in the tank, is a true result.
"In our latest batch of results, there is a 44 per cent spread in the gap between the tested cars' fuel consumption lab results and their on-road performance," he said.
"One 1.2-litre vehicle had similar on-road fuel consumption to several 2.0-litre cars, and a hybrid SUV had higher petrol consumption than a similar-sized conventional SUV."
Yet while much of the testing focus is on fuel consumption, the latest data also show that one of Australia's best-selling vehicles over the past five years, the Thai-built turbo-diesel Toyota Hilux, is a huge emitter of nitrogen oxides (NOx).
In fact, the test show the Toyota's current NOx tailpipe emissions in the real world were two thirds higher than is mandated by Australian regulations.
It produced 494 milligrams of NOx per kilometre. The current NOx standard for that vehicle under the Euro 5 Australian Design Rule is 280 mg per kilometre.
The Mazda BT-50 diesel ute was also a huge NOx offender. It produced 409 mg per kilometre.
Until the real-world testing program began, there was no way to independently test for emission nasties like diesel particulates and NOx and now the question arises as to whether any action by federal Transport will be taken for breaching the regulatory limits.
NOx is a collective term used to refer to nitrogen monoxide (nitric oxide or NO) and nitrogen dioxide (NO2).
In regional and low density areas, high concentrations of NOx are of less concern than in the city. But in places like Los Angeles, for instance, the gas phase reaction of nitrogen oxide in the atmosphere was a trigger to the city's terrible photochemical smog.
NOx also reacts with sunlight and hydrocarbon-produced radicals to form ozone.
The Toyota Hilux was Australia's top-selling vehicle for seven years until it was knocked off its perch by the Ford Ranger 4x4 last year.
There are tens of thousands running around Australia's major cities, and are popular as passenger vehicle substitutes.
