Car Tech: Smart mhd's stop-start technology saves petrol, Mother Nature

If there's one sure-fire way of urinating money up the wall -- figuratively speaking -- it's by owning a car. Luckily for cheapskates like you and us, Smart has unveiled a new version of its iconic supermini that reduces the cost of car ownership while not harming the planet -- much.

The Smart mhd, which we tested in this video, looks much like any 2009-model Smart Car. It uses Smart's new micro hybrid-drive technology, however, which switches the engine off as soon as you fall below a speed of 5mph under braking, and turns it back on again when you press the accelerator pedal.

Smart says the mhd system can improve fuel economy by approximately 8 per cent in mixed driving conditions and up to 13 per cent in urban environments, making it ideal for heavy traffic. According to Smart, the 71bhp coupe model can achieve 65.7mpg. It also spews just 103g/km of carbon dioxide into the atmosphere, versus the non stop-start model's 116g/km, which is good, but slightly too high to squeeze under the magic 100g/km marker that makes a car exempt from vehicle excise duty.

In practice, the Smart mhd works well. The stop-start technology feels a little disconcerting to begin with, and the 1-litre diesel engine does sound a little unrefined at high revs, but the overall driving experience is an enjoyable one. Our fears about engine wear seem unfounded, too, since the car's starter motor has been replaced with an electrically operated drive belt that gets its power from the Smart mhd's regenerative braking system.

The Smart mhd is by no means perfect. Its 0-60mph time of 13.3 seconds means all but the most apathetic of Sunday drivers will beat you off the lights, and the fact it only has two seats means most of your entourage will require their own transport. This aside, there's plenty of fun to be had. It's nippy in and around traffic, ridiculously easy to park, and the semi-automatic gearbox means you never have to worry about using a clutch.

The Smart mhd is available now for £7,060. You can watch a video of the mhd system in action by clicking play in the video thumbnail above.