What ever the testing regime, most drivers won’t achieve the test result. The current testing is as follow:
Urban cycle testing accounts for around 67 per cent of the test, while the extra-urban cycle accounts for the remaining 33 per cent.
The urban cycle consists of a lower average speed and is designed to simulate driving in a city environment with a constant element of stop/start driving at an average speed of 19km/h and considerable idle periods of around 30 per cent.
The extra-urban cycle is run at a higher average speed of 63km/h with a peak speed of 120km/h. It’s not an accurate representation of the regular fuel consumption on a highway, as the test isn’t conducted as a set speed over a period of time.
Driving with an average 63km/h with a peak of 120km/h possibly isn’t really relevant for those who tend to do most highway driving on the main highways where maximum posted speed limits are 100-110km/h. The 63km/h possibly is more like intraurban motorways where posted speed limits range from 70-110km/h and where there is likely to be some traffic where the average speed of a vehicle is significantly less than the posted limits.
I suspect that the 63km/h is used as it represents intraurban and some interurban movements. This is possibly where most vehicles do their extra-urban cycles as most of Australia’s car fleet is urban based (~90% if it correlates directly with Australia’s population urbanisation).
There is always opportunity to change the testing to better suit one’s particular driving pattern, but sure enough, the change is likely to be more different to another drivers driving pattern.
If one uses the values as a guide or standard benchmark to compare different vehicles at the time of purchase, it is suitable for that purpose (a vehicle with a ADR fuel use of 7.5L/100km combined will use less fuel than a 10L/100km combined cycle). What an individual actually gets will depend on a wide range of factors.
The above may also however bias towards lower fuel consumption from hybrid and PHEVs, where these vehicles use part of the onboard batteries to propel the vehicle. If a car owner does longer trips within a day (between charges), the fuel consumption is likely to be higher than the ADR test results as the (heavier) vehicle will mainly be propelled by the petrol engine potentially negating any perceived savings.