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Trends in Car Fuel Efficiency

This is an update of a (guest) post I did in December 2012 – I’m planning to keep updating it each year.

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.


“Lab tested” fuel efficiency for new vehicles: US trends

The EPA did a fascinating study on fuel efficiency trends in US vehicles manufactured between 1975 and 2013, available at Essentially, car engines became 50% more efficient over the 39-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 have been some significant improvements, as high oil prices hit home.

This is what happened to the fuel economy of new American vehicles between 1975 and 2013. Note that this is in “litres per 100 km”, so a lower number means a more efficient car. I’ve calculated the figures for cars, trucks and both of them combined and weighted by production.

US fuel efficiency trends for new vehicles


US fuel economy standards for new cars stayed the same for more than 20 years, but the Obama administration has begun to tighten them, starting with the 2011 model year, and with major incremental improvements proposed through to 2025.

I think it’s interesting to note, though, that fuel efficiencies started to improve again, well before the tighter CAFE standards began to came into effect. Americans began to shift towards more efficient cars of their own volition. They also started to buy fewer trucks. The market share for these massive vehicles peaked at 48% in the 2004 model year, and has now fallen back to 36%.


“Lab tested” fuel efficiency for new vehicles: New Zealand trends

NZ doesn’t have a long-term data series like the US, but the Ministry of Transport now collects 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. 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 these are directly proportional to the amount of fuel used.

NZ fuel efficiency trends for new vehicles


“On Road” fuel efficiency

The data I’ve shown above is lab-tested, and only applies for vehicles entering the fleet. There are a couple of factors to consider when applying it to the real world, and across the entire vehicle fleet. Firstly, cars tend to use more fuel on the road than the lab readings suggest (congestion and air conditioning being the two main culprits). Secondly, the data above is for cars being produced (or imported) 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 2013, it would still take quite a while before we’d see any noticeable difference to the fuel economy of our entire fleet of 3 million vehicles.

In fact, 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 decade (notwithstanding an apparent drop in 2012, which seems to be down to data issues: the MoT reckon the drop “seems too large to be credible”).NZ on road fleet wide efficiency

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.


So what are the takeaways here? New Zealanders (and Americans) have started buying more fuel-efficient cars thanks to higher fuel prices in the last decade, 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.

Most of our cars come from Japan, and fortunately they tend to be a bit more efficient than those in the US – 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.


22 comments to Trends in Car Fuel Efficiency

  • Kent Lundberg

    Jevon’s paradox?

  • Yes, exactly and the slow turn over of our fleet. Unfortunately only new car buyers will have the more efficient models.

    • NCD

      Why? Average Commodore driver could swap for a same year Honda Jazz and get massive (40%) reduction in fuel bill. There’s issues of status and Kiwi male identity (which seems stuck in the 70s) here.

        • NCD

          Maybe CSR needs to start with vehicle fleet? Maybe we need to be shaming large companies?

          • As someone who cycles and would love to see more PT and less driving, I don’t believe ‘forcing’ people into smaller, more efficient cars is useful. I do however, believe that our fuel tax could be higher but the only issue with that is the distribution of the funds under the current governing regime. Some people actually do need bigger cars (a Honda Jazz is not good at towing a boat for instance) and in the same way that we allow people to choose bigger, less efficient housing, the choice should be with the consumer but the scale of repayment should be scaled. Vehicle registration rates based on fuel economy, rather than type, could have a bearing on how people choose their cars?

      • Dan

        The thing is, petrol is still relatively cheap. So a 40% reduction in the fuel bill doesn’t mean the overall cost of the car is massively cheaper. Maybe doubling yr fuel efficiecy (halving yr fuel usage) will save you about $1000-1500 per year for an average driver. Loads of people will pay that extra fuel bill for a bigger/cooler/faster car. Often bigger cars are cheaper too, certainly in the 2nd hand market, so the total cost of the car is the same.

  • Matthew

    12kWh/kg is the energy density of petrol. Yet typically only 1% of that energy when burnt actually moves the driver. Li-Ion energy density is 160Wh/kg. Petrol then is 75 times more energy dense and then they go and waste it on 1.5 tonnes of steel.

    The Nissan Leaf has 24KWh of battery with a curb weight of 1,521kg. Of which the batteries are about 150kg.

    At the other end of the spectrum are pedal powered, enclosed, recumbent tricycles called velomobiles weighing 30kg that easily get to 40km/hr under human power. They could easily be engineered with Li-Ion batteries to go 60km/hr and have ranges of 200km+ with total weights of under 40kg.

    And in between there are things like this: 300kg 3 wheelers –

    We as a society really don’t need Ford F150 trucks and Holden Colorados. We need innovative design with current battery technology and a few smart entrepeneuers who don’t have the rusty, prehistoric attitudes of car companies. “Cars” should weigh the same as a prop, and not the whole rugby team.

    As for getting around a city – riding a foldable push scooter like a kids scooter with 300Wh of battery and a 150W motor (which all up costs less than $500) that you can fold and take on the train, and a fast frequent electrified railway is all anyone really needs.

    • I could not operate with out a AWD wagon of some sort. At present I have a Nissan X-Trail (petrol). With all my day to day requirements loaded it has averaged 9.1l/100km over 50,000 km’s. I could not operate out of a Leaf (or a Volt, which I prefer, for that matter).

      • MFD

        For some of us the motor vehicle is a tool of the trade; we have a battered old Hilux for orchard work and 2 other vehicles for family and business use. A Leaf to replace one of the family cars and to be used as the vehicle of preference is highly feasible for our requirements. When it comes to selecting vehicle characteristics my priority is generally type of duty required, safety (crash rating), reliability (as well as that can be determined), depreciation, roadholding then maybe fuel economy.

        I have owned a few AWD wagons in the UK and US. All Subarus and all good but not great for fuel economy. I understand that recent engine design changes have resulted in improvements.

      • Matthew

        Bryce, Yep it is a useful vehicle, but it does seem like overkill if you’re just going to the shops.

        I have a car with a 3.5l petrol engine and get 8.7l/100km out of it. I am nursing it from WOF to WOF and hope to get something smaller in a couple of years. I too think I’d be lost without having access to far off trailheads, and I take my bikes on the back to go riding places.

        I also have an electric bike with panniers which I can put a lot of groceries in (but usually get the groceries in the car when coming back from other things), and a foldable kick scooter for taking on the train.

        I’d love a vehicle somewhere in between the size of my car and my bike for most daily commuting to the train station and running into town and stuff. I’m 20 minutes from town on my bicycle. 10 minutes by car. I’m too far from work to commute by bike, but my girlfriend commutes on it to her job.

        It does seem there is a massive untapped market for anyone coming up with a small highway speed electric vehicle with a decent range at a reasonable cost.

      • Dan C


        When i was in Kashgar, China recently, 95% of the population seemed to get around on electric scooters. Like your honda Nifty Fifty but electric instead of petrol, and cheap.

  • MFD

    Those are published fuel economy figures. Real-life figures differ depending on factors such as tyre pressure, use of AC, driving style etc. Substantial fuel economy improvements can be gained just by avoiding short trips from cold as there is a fixed fuel hit to heat up the engine block, manifolds. coolant etc. VW’s foray into small engines with turbo or supercharging is interesting in this respect. Less phyical and thermal mass and, of course, electric vehicles avoid this altogether.

    • Twincharging has its roots in the 1980s, although for entirely different reasons, but the idea of generating more power from smaller blocks isn’t new and we’ve had the technology to do so for some decades now. I’d be interested to see how these figures adjust for more common use of automatic boxes and congestion idle time. As far as electric vehicles are concerned, I would love to be able to build an electric car like I could build the ICE version of my favourite car, but the end user components are too expensive by a factor of ten and the end result wouldn’t be worth it.

    • Dan C

      Yes i’ve always wondered why turbos never caught on in the petrol world outside of performance models, but has been mainstream for diesel engines for donkeys.

      No way i would get great acceleration for overtaking and still return 4.5l/100km when crusing in my car if it wasn’t a turbo.

  • Bryan Sellars

    Jervons paradox applies (unless prices of fuel rises) as efficiency goes up so do miles, with higher oil prices US consumption had dropped 4% but since the lower prices this year is rising at 7%, unless we ditch the car and find better ways to commute we will travel down the road of ever diminishing returns.

    Comparing my travel to work back in the 1950’s it was no longer than motorist’s take today on congested roads, but I and the friends I made by commuting on the same trains year in year could read the paper or chat and if we were tired we could have sleep and know we would be woken at the destination, how different today, with drivers stressed and a bag of nerves, road rage and aggression what a world the car has created and then we claim to be intelligent seems a bit dumb to me.

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