Auckland Transport Blog

This is a guest post from commenter JohnP

These days, most people are aware (often painfully so) of petrol prices being over $2 a litre, and much higher than they were a decade ago. It costs more to run cars than it used to, and consumers’ wallets haven’t really kept up with the cost increase. Unsurprisingly, there’s a heightened awareness about fuel efficiency, which we could also call “fuel economy” to highlight the fact that people are generally more worried about the cost implications.

The EPA did a fascinating study on fuel efficiency trends in US vehicles between 1975 and 2011, available at http://www.epa.gov/otaq/fetrends.htm. Essentially, car engines became 40% more efficient over the 36 year-period. However, over this time, cars became much heavier, needing more energy to move. US cars became more efficient from around 1975-1985 as the oil shocks hit and the government started to regulate fuel economy (the Corporate Average Fleet Economy scheme, still around today). Then, fuel economy actually got worse for 20 years – engines were getting more efficient, but this Americans were driving increasingly heavy cars, and switching to SUVs (or “trucks” as they call them in the US) in their millions. Since 2005, there’s been some improvement again, as high oil prices hit home.

Incidentally, Obama’s administration have tightened up US fuel economy standards for new cars starting in 2011, the first time this has been done since 1985. The improvements over the next 13 years will be major, assuming the Republicans don’t overturn them. Which they probably will.

Source: EPA, John Polkinghorne

We don’t have a long-term data series like the US, but I would imagine that fuel economy in the NZ car fleet has followed a pretty similar path. Information from the Ministry of Transport shows that the NZ light vehicle fleet has on-road fuel economy of around 10 L/ 100 km, and this has remained stubbornly flat over the last eleven years.What’s the relevance for NZ? Well, most of our cars come from Japan, and fortunately they tend to be a bit more efficient – not that it’s helped us much. But we’ve jumped on board the SUV bandwagon, and we’ve got a higher proportion of those in our fleet than just about any other country besides the US. We’re also madly in love with big cars like the Holden Commodore and Ford Falcon. The average engine size for NZ cars is a pretty hefty 2.4 litres.

Source: Ministry of Transport annual vehicle fleet statistics

If we take a look at some Australian data, we can see that they’ve actually had no improvements in on-road fuel efficiency in the last fifty years. Australia’s a fair bit hotter than NZ so we can imagine that they took to air conditioning like a shrimp takes to a barbie.Two things to note there – firstly, the MoT data shows “on-road” fuel efficiency, or what our cars have actually achieved on our roads. The US data shown above is lab-tested, and cars tend to use more fuel on the road (congestion and air conditioning being the two main culprits). Secondly, the US data is for new cars produced in each year, so those fuel economy values can change much quicker than when you’re looking at the total fleet, as for the NZ data. If Priuses were the only new cars sold in New Zealand in 2012, it would still take quite a while before we’d see any noticeable difference to the fuel economy of our entire fleet of 3,000,000 vehicles.

Source: http://www98.griffith.edu.au/dspace/bitstream/handle/10072/29806/60756_1.pdf?sequence=1

More recently, New Zealand’s Ministry of Transport has started collecting fuel efficiency ratings for vehicles as they enter the fleet. This shows that the light vehicles coming into New Zealand (including cars, vans, light trucks etc) have been getting more efficient, which is a good thing. Cars entering the fleet today are at least 10% more efficient than in 2005, on average. You can see the downward trend in fuel use in the graph below. Actually, the graph shows CO2 emissions, but as we’ll see in my next post, these are directly proportional to the amount of fuel used.

Source: Ministry of Transport quarterly vehicle fleet statistics

So what are the takeaways here? New Zealanders have started buying more fuel-efficient cars thanks to higher prices since 2005 or so, but the improvement hasn’t been stunning – 10% is nothing to write home about, and there hasn’t been any noticeable effect on how much petrol the overall car fleet uses. In fact, international comparisons make it likely that decades of technological progress have done almost nothing to reduce how much petrol we use. Engines have gotten better, but cars have gotten bigger.