Instead of a conventional starter and an alternator, the smart fortwo mhd works with a belt-driven start/stop generator that uses the engines "idle phases" as efficiently as possible. The mhd switches the engine off as soon as you brake and fall below a speed of 8 km/h. When traffic gets moving again release the brake pedal and the engine starts again in the fraction of a second allowing you to continue your journey.The smart fortwo mhd's start/stop generator enables you to make petrol savings of up to 20%[1] in urban traffic, without compromising on performance. The system has been perfected for the smart fortwo's automated manual transmission and is fully automatic, i.e. no gear shifting or clutchwork are necessary and you do not need to do anything out of the ordinary.However, less petrol and CO2 do not mean that you have to compromise on comfort. No matter which equipment line you choose – they are all available with mhd technology. This particularly environmentally friendly drive comes as standard for the two 45 kW and 52 kW petrol engine versions.Combined fuel consumption for the smart fortwo micro hybrid drive coupé with a 45 kW (61 bhp) petrol engine in l/100 km[3] 4.3, combined CO2 emissions in g/km[3] 103[4].Combined fuel consumption for the smart fortwo micro hybrid drive coupé with a 52 kW (71 bhp) petrol engine in l/100 km[3] 4.3, combined CO2 emissions in g/km[3] 103[4].Combined fuel consumption for the smart fortwo micro hybrid drive cabrio with a 52 kW (71 bhp) petrol engine in l/100 km[3] 4.4, combined CO2 emissions in g/km[3] 105[4].