See also:

ConnectedDrive or BMW Assist
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Maintaining/storing the speed
Press the button*. When the system is switched on, the current speed is maintained and stored as the desired speed. It is displayed in the speedometer and briefly displayed in the instrument ...

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 ...