Efficient Motorway Driving

I’ve been experimenting with using 10 percent less (use10percentless) for a some time now and trying to find efficient motorway driving styles. As my job has me going between Paris and London regularly these days, I’ve had plenty of opportunities to experiment. I was finding it hard to reduce fuel consumption, but now I think I’ve cracked it.

You might be wondering why I’m talking about “Efficient Motorway Driving” on a site called “Life in the Right Direction”. Well, I believe that the right direction in life is one based on love (mostly in the form of respect and compassion) – love for ourselves, each other, every thing, nature and the world. Trying to consume and pollute less is very much in line with love for the world and each other.

Efficient motorway driving - autoroute

Rapid recent progress with efficient motorway driving

As you can see on the graph below, between July and November this year I’d driven between the UK and Paris many times and was struggling to find ways to use less fuel. For many months, my fuel consumption was quite flat and staying around 25 litres per trip. If anything, the fuel consumption was going slightly upwards, even though I was trying to bring it down.

The drive between my home in France and the office in the UK is almost exactly 400 kilometres and I was driving a 2.0 litre diesel Volkswagen Passat. The motorway speed limit in France is 130 km/h and between July and November my practice was to do 130 km/h or a little above (the speedometer slightly underestimates the actual speed) making use of the car’s cruise control function. I was experimenting and monitoring the effect of weight in the car (mostly the number of people), having the air-conditioner on or off, driving very efficiently in built up areas (see Using less fuel while driving), weather conditions and the like, but all these seemed to have an almost immeasurable effect based on the statistics I’d collected.

Two factors that have a dramatic difference are average speed and traffic, and there’s a third surprising factor that might be very important as well.

Efficient Motorway Driving - Fuel used driving from office (UK) to home (France)

Average Speed & Traffic – Efficient Motorway Driving

Efficient motorway driving means not driving too fast. There’s a price to pay for a faster speed, it takes more energy. If you want to drive faster you have to push the accelerator pedal a bit more and burn some more fuel. It only stands to reason that you have to burn more fuel to produce more energy to make the car go faster. Slower is more energy efficient.

I made the full 400 km trip keeping the cruise control set on 120 km/h instead of 130+ km/h and I began to notice a immediate improvement in fuel consumption.

The third last dot on the graph above (7/11/14) was my first experiment with 120 km/h plugged into the cruise control. On this day I didn’t really see any benefit because I hit a big traffic jam near Paris. The traffic jam added 30 minutes to my trip and the extra fuel used to get through this seemed to wipe out the benefit I would have gained.

The second last dot on the graph above was the first experiment with 120 km/h in the cruise control without any traffic issues. Now I saw a significant drop. It was more than 15% less fuel usage. That’s great and it satisfies the use10percentless initiative easily. The only problem is being satisfied driving a little bit slower.

The next step – shutting off the cruise control

My next experiment was to try the drive without the cruise control. I tried this because of a comment I read on this page on polluteless.com which said;

  • Turn off cruise control in hilly areas.
    • Cruise control keeps your car at a constant speed. If you get to a hill your vehicle’s computer senses the natural slowing down of the vehicle and increases the fuel flow to the engine and possibly even shifts down to continue with the programmed cruise speed. That uses a lot more gas. Drive without cruise control and let your car slow down at an uphill.
  • Use cruise control where it is flat.
    • Cruise control keeps the car at a constant speed much better than you can do it in a flat area. Little variation of speed means less gas consumption when it is flat..

This was a real surprise to me. Who would have thought that a cruise control function could cause more fuel to be burnt. It’s supposed to be a modern marvel of convenience for long driving trips. Reading this prompted me to run my own experiment.

The very last dot on the graph above is the experiment that I did without using cruise control for the whole journey. I actually changed a few things at the same time. I regulated my speed between 100 km/h and 120 km/h. When going uphill, I allowed the car to slow down to 100 km/h but never any slower. When going downhill or flat I allowed the car to speed up to 120 km/h but no faster. So the average speed would have been somewhere around 110 km/h.

The overall result was almost 30% reduction in fuel usage compared to the earlier average when driving at 130+ km/h with cruise control. The last experiment wasn’t very scientific because I changed two things at once. It’s impossible to determine the relative importance of the driving style and the average speed.

Nevertheless, it’s amazing that reducing average speed and adjusting driving style can cut fuel consumption by almost 30%. That’s much more than I would have expected.

Where to now with efficient motorway driving?

These specific experiments have now come to an end because I have had to turn in the car I was using and I’ve bought a new one in the UK. I’m about to start collecting new data and begin new experiments with this new car.

For sure, slower motorway driving and adapted driving styles are here to stay for me. I imagine that a lot of people are thinking that driving slower is boring and takes too long. My experience with this is a little different.

Driving fast is really a prison. Let me explain. When you drive fast and want to overtake many other cars, you get caught in the rush and in wanting to arrive quickly. You have a lot of cars to overtake. Even faster cars come up behind you and you have to find ways to let them by while still overtaking slower cars. Some cars are just a little bit too slow so you speed up a bit more to get past and your speed gradually gets faster and faster.

It’s like you’re on a hamster wheel going quicker and quicker, getting stressed and worrying about whether you’ll arrive at your pre-determined estimate of what would be a good time.

The opposite is to settle on a comfortable speed, sit in the slow lane, let all the fast cars just pass by.  Occasionally you’ll need to overtake other cars or trucks and if faster cars are around too, you don’t mind easing back a bit more until it’s clear and safe to overtake. You have a realistic arrival time in mind (which could be 30 minutes or so later than otherwise) and little stress or worry.

When I settle into a long trip at a slower speed, it actually feels very liberating. The drive seems to pass by very peacefully and I arrive much more relaxed and energetic. So, the advantage of arriving a bit earlier by driving fast is dissipated by the fact of arriving more stressed and tired.

Adding to all this, driving more slowly and calmly uses less fuel, pollutes the world less and saves us money (not even mentioning lower accident risk). The only negative is that it takes a bit longer. Seems like a very easy decision to me.

Do you have any tips for efficient motorway driving?

Related Links – Efficient Motorway Driving

4 Responses to “Efficient Motorway Driving”

  1. Ian Fisher

    The most effective fuel efficiency tactic, by far, is driving at 100km/h (60mph)

    Sadly, at that speed, it is very likely that you are reducing other motorists’ efficiency more than your own increase.

    On a recent trip between Houston and San Antonio, 104kmh/65mph felt like the minimum. In a twelve year old car, we got 36 miles per US gallon (45 miles per gallon in other measures).

    Not bad!

    • Pete

      Hi Ian,

      That is good mileage for a car in Texas. I would have assumed that Texas cars would get nowhere near that.

      My dream is a day when all drivers decide to drive a bit slower for the sake of burning less fuel and creating less pollution. Then one person trying to do that wouldn’t impede anyone else. At the moment the TV advertising is encouraging us to buy powerful cars with “muscle” and drive them like “cars are supposed to be driven” – it’s a little bit like making sure you have a good looking gun while playing Russian roulette (I’m exaggerating, I know).

      Thanks for leaving the comment.

  2. Liese

    We both drive a Prius, ’cause once you see a fuel usage of 50+mpg nothing less than electric will suit. We drive by mostly coasting and driving no more than 60mph (in the slow lane) on the highway. In rebuttal to Ian, since most everyone is driving significantly over the speed limit you will always get passed by so you might as well sit back and enjoy the journey, as well as the fuel savings and knowing you’re not adding as much carbon. Be the change as they say.

    • Pete

      Good to hear. Thanks Liese. Isn’t is strange how most people are concerned about climate change and global warming, but they also try to go as much over the speed limit as they can get away with? If everyone just slowed down a bit we’d go a long way toward stopping global warming. Obviously people don’t care much about the environment or, maybe more truthfully, they want other people to fix the problem not themselves.

      By the way, I drive a fully electric car now and loving it.


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