The pervasive inclusion of electric vehicles on our roads is already a reality and is here to stay in the future. Many car manufacturers are including full electric or hybrid models in their catalogues and more will come in the near future. However, since the electric vehicles’ range is still insufficient to compete with combustion-engine vehicles, for many electric vehicle owners reducing energy consumption, in order to increase available range, has become a matter of increasing concern. This paper is based on previous work conducted as part of the European Commission project ecoDriver. EcoDriver’s main purpose is to teach efficient driving strategies and facilitate drivers’ decision-making processes through several feedback modalities, in order to help increase driving efficiency. Here, the Full ecoDriver System combined with a haptic feedback gas pedal was tested in real driving conditions. In this paper, the drivers’ subjective assessments in terms of effectiveness, workload and acceptability are presented. The sample profile was composed by thirty young but experienced drivers who had to drive around an open track which allowed several possible scenarios. The main results suggest that the system effectiveness depends on the event type and the feedback modality provided. The haptic feedback did not increase workload compared to visual feedback, however, as a prototype, it showed some acceptance constraints. Results presented in this paper advance further research concerning human factors in eco-driving and haptic feedback systems research.