Auditory messages for speed advice in advanced driver assistance systems

Simple tones in in-car systems are mostly used for status indication or warning and alerting purposes. We argue that simple tones can also be used for the purpose of advising drivers through an Advanced Driver Assistance System (ADAS). Our ADAS application is called Cooperative Speed Assistance (CSA), where drivers receive advice to slow down or speed up to coordinate their speed with the speed of other vehicles in the traffic. Two concepts of auditory messages are presented: Looping messages are played as long as the advice applies, while Toggle messages mark the beginning and the end of an advice. For each concept, two prototypes of simple-tone signals were designed based on existing guidelines about sound characteristics affecting urgency and evaluation by users. The temporal characteristics of the signals indicated how much or how fast drivers should adapt their speed. The concepts were evaluated by having users drive in a driving simulator. Objective measurements indicated that there was no difference in effectiveness between the two concepts. Subjective evaluation indicated that users preferred the Toggle concept.