Automobile manufacturers are making information systems available in all vehicles. Mostsystems are screen based, but increasingly systems are either hybrids (screen/speech) orspeech based. Speech systems in vehicles may have advantages over screen based in-vehiclesystems; literature suggests that speech can be less distracting than screen-based interactions.Nonetheless, using speech systems in the car also introduces social and attitudinal effects.Voices are not neutral! Voices carry socio-economic cues including indicators of gender, age,personality, emotional state, ethniticity, education and social status. Perception ofinformation presented by the voice is influenced by the perception of the voice demographics.This is further complicated by different individuals perceiving voices in different ways. A voicethat is seen as positive by one individual can be perceived negatively by another. We presentresults from a number of driving simulator studies of speech based in-vehicle systems. These studiesshow that speech based in-vehicle systems can affect drivers’ attitude and drivingperformance. Attitude and performance can be improved, but the effect of the voice can also proveharmful for driving behaviour and driving safety. This makes it important to include the voice as adesign parameter of speech-based in-vehicle systems.