The growing introduction of new technologies inside vehicles represents a set of extra information sources. Its use can interfere with the driving activity and induce performance decrements. An on-road experiment was conducted to investigate how drivers reacted to the simultaneous interaction with in-vehicle systems. Forty-eight subjects (elderly, reference and novice) participated in the tests. They were asked to interact with one (road guidance system) or two (road guidance system and mobile phone) on-board devices. Their performance was evaluated for the turn left manoeuvres and main effects of system conditions were revealed. The simultaneous interaction with both in-vehicle systems induced participants to some performance decrements on the driving task: higher number of late activations of the turning indicator; lower mean speeds before the intersection; lower values of instant speed at the beginning of the turn manoeuvre; higher steering wheel variability; activations of the braking pedal with less pressure, later, and performing a higher number of strokes; and also less glances towards important areas of the environment. No significant difference was observed for the guidance task. The comparison between driver groups' performance did not reveal enough significant differences in order to draw a general conclusion.