Car companies will be scrambling to avoid embarrassment as the real world-testing of car fuel consumption and emissions by the Canberra-based Australian Automobile Association begins releasing its results next month.
A pilot study of 30 vehicles undertaken by the association six years ago found that on average, those tested consumed an average of 23 per cent more fuel than stated by the manufacturer - 21 per cent higher for diesel vehicles and 24 per cent higher for 16 petrol vehicles.
The then sole plug-in hybrid vehicle used a whopping 166 per cent more fuel when fully charged and 337 per cent more when its battery was depleted.
The $14 million program independently will test 200 cars, utes and EVs over the next four years to see whether their fuel consumption and emissions of CO2 and noxious materials are the same when cars are driven in real-world conditions as they are in the laboratory.
All the results will be published and posted on the website realworld.org.au. Results will start to drop into the website in November.
The association's managing director Michael Bradley said car buyers had for too long been misled regarding their vehicle's fuel consumption and environmental performance.
"This program will deliver truth in advertising and drive down demand for cars that over-promise and under-deliver," he said.
"Better information will enable families and fleet buyers to buy vehicles that will meet their budget and environmental requirements."
One of the world's biggest scandals involving a global car company deliberately using a software program to manipulate emissions results erupted in late 2014 when university researchers in the US detected a significant anomaly in the emissions they were getting from a two-litre diesel-powered Volkswagen passenger car outside the laboratory.
The "Dieselgate" scandal - ostensibly a corporate fraud - became a global phenomenon in 2015 when the US Environmental Protection Agency (EPA) served a notice of violation on the company.
It found that when the cars were operating under controlled laboratory conditions the device appeared to have put the vehicle into a mode in which the engine ran below normal power and performance. Once on the road, the engines switched out of this test mode.
It caused more than 10.5 million cars to be recalled, owners compensated and the chief executive Martin Winterkorn resigned, describing how "deeply sorry that we have broken the trust of our customers and the public".
Engineers involved were jailed and the scandal cost VW over $10 billion, as well as serving a massive blow to its corporate reputation.
The AA said that the Volkswagen emissions scandal first showed that real-world testing was needed, as stringent emissions regulations around the world were incentivising carmakers to optimise their vehicles' fuel consumption and emissions performance for the laboratory tests used for regulatory compliance.
All the "real world" testing will be done in Victoria. Vehicles will drive in real traffic on urban and rural roads, as well as dual-lane highways. Each testing vehicle will be fitted with portable emissions measurement equipment.
During test drives, this equipment records tailpipe emissions of greenhouse gases, as well as pollutants that affect air quality, such as carbon monoxide, oxides of nitrogen (NOx) and solid particles.
Fuel consumption will be calculated from the data collected.
The new program comes as the federal government is poised to roll out a new fuel efficiency standard for all vehicles after Australia has fallen well behind the stricter standards of the US and Europe. Car companies want a slow roll-out of the new standard over concerns of how it will affect sales and the availability of vehicles to consumers.
