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Green driving can halve fuel use

words - Jeremy Bass
US study suggests eco-driving practices can make nearly real world fuel economy
Hold the front page – better driving practices can halve your fuel use! It may read like mere confirmation of the obvious, but research by the University of Michigan's Transportation Research Institute has confirmed that picking the right vehicle for one's purposes and driving it the right way can save you fuel – and a load of money.

More importantly, the study gives a value to each element of vehicle choice and driving. When added up they produce a conclusion that the difference in fuel economy can be as much as 45 per cent.

There was no shortage of cause for alarm in the figures UMTRI researchers Michael Sivak and Brandon Schoettle delivered in their paper, 'Eco-driving: strategic, tactical, and operational decisions of the driver that improve vehicle fuel economy'.

Think engines have become more efficient over time? Maybe, but not by that much -- at 17.4 mpg (13.5L/100km) average fuel consumption for all US road vehicles in 2008 was only 25 per cent better than the 1923 average of 14.0 mpg (16.8L/100km). Taking current average loads and journeys, the study stated: "driving a light-duty vehicle in the US... is more energy intensive than flying, not to mention using a bus or a train."

Sivak and Schoettle claim the single most important factor is vehicle choice. The thirstiest vehicle on sale in the US consumes on average nine times more fuel than the most frugal.

Weight is also is also among the chief contributors and this isn't just about porky SUVs... Sivak and Schoettle also factor in America's obesity epidemic, citing an increase in national average adult weight of about 24 pounds (about 11kg) between 1960 and 2002 – enough by their calculations to boost fuel consumption by about 0.5 per cent.

The report gives endorsement to car-pooling and sharing with the conclusion that a 30 per cent drop in vehicle occupancy since 1960 has produced a commensurate rise in vehicle energy consumption of around 30 per cent per occupant.

Other factors they mention include route selection, cargo load, vehicle maintenance and drivers' road behaviour. Taken in aggregate, these factors can penalise individual drivers by up to 45 per cent in fuel economy. Which is to say, by Sivak and Schoettle's calculations, a car nominally good for 36 mpg (6.5L/100km) will see fuel efficiency drops in the order of 45 per cent to 19.8 mpg (11.9L/100km) under command by drivers who fail to observe a basic set of ‘eco-driving' recommendations.

"Eco-driving includes... strategic decisions (eg vehicle selection and maintenance), tactical decisions (eg route selection), and operational decisions (eg driver behaviour) that improve vehicle fuel economy," they say in their statement.

Within these categories, they break down each element into a series of choices and behaviours, giving each an approximate value in fuel consumption. For example vehicle maintenance issues include regularity and skew of engine tuning (an out-of-tune engine can cruel fuel efficiency by 4-40 per cent), tyre selection affecting rolling resistance (1.5 per cent for tyres under inflated by 5psi) and maintenance and choice of engine oil (1.2 per cent for wrong oil).

Tactical decisions for drivers include road choices, which affect speed limit, stop-start regularity, topography (15-20 per cent) and congestion.

On the operational front (read: driver behaviour), they pin a 30 per cent penalty on high road and/or engine speeds, and a further 20-30 per cent on aggressive driving habits. Air conditioning costs 5-25 per cent, while failure to use cruise control at highway speeds costs a further seven per cent.

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 Published : Tuesday, 13 September 2011
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