We present a novel in-vehicle sonification for providing immediate feedback about the current vehicle speed in consideration of prescribed speed limits and common driving practices. The key conceptual idea of our ``Slowification'' auditory display is to assume that the sound of the car (i.e.~the car's audio system) travels with the allowed (or expected) speed and to virtually position the driver into this space according to the car's current speed,resulting in a sound which moves to the back as one drives faster than allowed and catches up on slowing down. Further changes of the sound for excessive deviations complement this design.

We evaluated the Slowification system in a virtual reality based car simulator delivering realistic soundscapes of both engine and media sound placement, showing that it indeed helps the user to drive within speed limits and additionally provides less distraction than a conventional visual speed display. Questionnaire results furthermore indicate that users easily accepted this novel auditory display as an unobtrusive in-vehicle user interface.