An automobile start-stop system or stop-start system automatically shuts down and restarts the internal combustion engine to reduce the amount of time the engine spends idling, thereby reducing fuel consumption and emissions. This is most advantageous for vehicles which spend significant amounts of time waiting at traffic lights or frequently come to a stop in traffic jams. Start-stop technology may become more common with more stringent government fuel economy and emissions regulations. This feature is present in hybrid electric vehicles, but has also appeared in vehicles which lack a hybrid electric powertrain. For non-electric vehicles fuel economy gains from this technology are typically in the range of 3-10 percent, potentially as high as 12 percent. In the United States, idling wastes approximately 14.8 billion liters (3.9 billion U.S. gallons; 3.3 billion Imperial gallons) of gasoline per year.
On a manual transmission vehicle, stop-start is activated as follows: Stop car and press clutch - move gear lever to neutral - release clutch - then the engine stops. The engine will not stop if the car is moving, even if the aforementioned steps are followed (this is not true for all cars). The engine restarts when the clutch is pressed prior to selecting a gear to move the car. The engine may also restart if there is a demand for power from, for example, the air conditioning system.
Since automobile accessories like compressors and water pumps have typically been designed to run on a serpentine belt on the engine, those systems must be redesigned to function properly when the engine is turned off. Typically, an electric motor is used to power these devices instead.
This technology has also been used on Honda scooters in Asian markets for the last decade. Their PCX 125:cc model was released in 2010 to be sold in Europe with this technology, though their North American model does not feature it.