See also:

Switch off the engine during longer stops
Switch off the engine during longer stops, e.g., at traffic lights, railroad crossings or in traffic congestion. Fuel savings are achieved after the vehicle is switched off for only approx. 4 s ...

ConnectedDrive or BMW Assist
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Switching off automatically
System switches off: above approx. 9 mph/ 15 km/h. Switch on the system again if necessary. ...