Honda is making a big deal about how its new Insight has been designed with less focus on getting the best result in the official fuel economy tests, and more on real-world economy.
Whether or not that is PR bluster is a different discussion, but it does raise an interesting point about how the official figures are calculated.
Firstly, they are not measured on the road, but in a lab on a rolling road, and not by calculating the actual fuel used, but the exhaust emissions and from that working out the economy.
The car conducts two routes, over a total distance of just 6.8 miles. All of which is on the flat. The urban figure is measured over 2.5 miles, at a maximum speed of 31mph and an average of 12mph. The extra-urban test is 4.3 miles at speeds of up to 75mph, but averaging 39mph. The combined figure is simply a weighted average of the two.
The tests are run without air-con, lighting or audio equipment and, because the tests have to accommodate commercial vehicles, the acceleration components allow 50 seconds to reach 62mph, which is not how most people drive.