A haptic pedal has been designed to emulate the behaviour of a common vehicle pedal and render superimposed vibrations with different characteristics. It was installed in a driving simulator, as an accelerator pedal with the secondary function of a vibrotactile Frontal Collision Warning (FCW). The efficacy and feeling of this solution was tested with 30 subjects using vibrotactile signals with 0.50,1.05, and 1.60 Nm, at 2.5, 5, and 10 Hz, against a baseline visual FCW. Participants had to match the speed of a leading vehicle when the FCW was triggered. Their braking response was evaluated in terms of brake reaction time, matching speed time, control of velocity and headway reduction. Driver's feelings were assessed with Kansei methodologies. Haptic stimuli were found to be more effective than visual signals, and the characteristics of the vibration also influenced the results. The best performance was achieved at the maximum amplitude, and in the range between 5 and 10 Hz. The perceived functionality and discomfort followed a trend coherent with the objective measurements. The conclusions of this study may be applied to develop effective and safe warning systems in vehicles, limiting the annoyance that they might cause to drivers.