SOME people always take things to extremes. For those trying to save fuel there is hypermiling, in which the really dedicated try to use less than 4.5 litres/100km (ie, travel more than 80 miles on a gallon) in a car that under normal use might do only half as well. Apart from driving very slowly and trying not to use the brakes (which dissipates energy), hypermilers employ other tricks, such as wiring the fuel injectors up to lights mounted on the dashboard so they can see whether or not they are squirting fuel into the cylinders. Although this is all too much trouble for most motorists, the hypermilers do have a point: driving technique plays a big part in how much fuel a car consumes. Now various devices are being used to help teach more moderate ways of driving economically.

Not surprisingly, companies that operate fleets of cars and trucks are among the first users of fuel-saving “eco-assist” systems. The most popular of these are global-positioning system (GPS) units that use live traffic information and other data, such as weather and past trends, to plot not the fastest but the most economical route to a destination at a particular time. According to iSuppli, a Californian research firm, fewer than 1% of new cars have such “eco-routing” systems fitted, but it expects that by 2020 a third will.

Interest is also growing in other devices that go beyond a simple fuel-economy meter and provide more information about drivers' behaviour. One such is used by Masternaut Three X, a British company that specialises in vehicle tracking. It taps into the engine-management system which, because of the increasing amount of electronics used in cars, contains data that can be analysed to monitor such things as excessive revving and harsh braking. This information can be shown as a series of warnings on the dashboard and is monitored by fleet managers. Firms using such systems say they can yield fuel savings of around 10% a year.

As well as discovering those with the heaviest feet on the accelerator pedal who could do with retraining, this can also help reduce accidents. “There is a correlation between driving efficiently and safely,” says Dan Steere, chief executive of GreenRoad, a company based in California. For instance, driving more smoothly by anticipating manoeuvres and then braking and accelerating lightly not only uses less fuel but also tends to make drivers more alert to avoiding potential accidents.

GreenRoad's driver-monitoring device does not need to tap into the car's innards. It uses GPS to measure a vehicle's speed and a set of accelerometers to measure the forces acting on the car as it accelerates, brakes and turns. The data are analysed to determine how the vehicle is being driven and the results shown to the driver as green, amber and red LEDs. For fleet cars, the data can also be relayed to a control centre, so that Big Brother can tick off offending drivers.

Mr Steere claims that despite the Orwellian overtones most drivers will soon become comfortable with the device and value the fuel savings it offers. He has clearly never met Jeremy Clarkson.