Presented at First international conference on driver distraction and inattention (DDI 2009), Gothenburg, Sweden, September 28-29, 2009

The aim of this study was to better understand how may differ conversing by phone and conversing with a passenger by comparing the driver’s speech in both conditions. Sixteen drivers (from 21 to 50 years old) participated in an on-road experiment on motorway. Naturalistic conversations were performed in 3 conditions: car stationary, while driving under Low or High attentional demand. Speech indicators such as speech rate in words per minute, number of hesitations and repetitions per word were investigated. Phoning was revealed as being more complex than conversing with a passenger as shown by a decrease in speech rate and an increased number of hesitations and repetitions. Results also showed the negative influence of the driving condition complexity on the speech quality.