Abstract
Failure to control driving speed puts drivers and others in a hazardous situation. In addition to speedometers and other advanced technologies, drivers can also determine their driving speed through sensory channels. Correct estimation of driving speed plays important roles on road safety. It is also important to sense changes in speed. In-car sound is an auxiliary cue often neglected. There are three parts in this study. First was to explore human speed perception through in-car sound and find useful sound elements by separating sounds into different frequencies. Second was to combine simulated windscreen views and real in-car sounds to examine eligible drivers’ performance in the perception of speed changes. The last was to explore how music influence speed perception by having in-car noise as cues. The results of the first part showed a serious underestimation at high speeds. Quiet cabin leads to speed underestimation. However, weakening intensity of frequencies below 600 Hz which descended as speed increased (against overall pattern) helped improve estimation performance especially at higher speeds which is most underestimated with normal sound. The results of the second part showed that drivers were poor at detecting speed changes. The results showed that only 52.36% of the participants noticed speed changes, and they required an average of 8.75 seconds to respond. Providing in-car sounds, especially clear, vibrating noises, can improve driver performance. And the results of the third part showed that music tempo influenced drivers’ speed perception by providing more temporal information and thus make speed perception faster. And the volume of music has no direct relationship with speed perception and works as a mediating factor between music tempo and speed perception. We suggest that vehicle designers should maintain a minimum level of in-car sound, and road designers should provide auditory cues on certain road sections to improve road safety. This study can contribute to soundproofing design in vehicle industry by suggesting that specific sound frequencies be preserved while irrelevant ones are weakened. In this way driving safety and vehicle quietness could be achieved at the same time.