The research presented in this dissertation focuses on supporting drivers in the longitudinal control of their vehicle during car-following. The goal of the research is the human-centred development of a haptic gas pedal interface that comfortably supports drivers in maintaining a safe separation with a leading vehicle during car-following. Two different approaches were found to be suitable for implementation as haptic information providers through the gas pedal. The first approach was to add a force to the gas pedal dynamics which would have to be related to the safe-field-of-travel ahead of the own vehicle and changes therein. The gas pedal dynamics, that is, the force/pedal-position relationship is not changed by this approach. The second approach was to change the stiffness of the gas pedal by adding a virtual stiffness to the inherent stiffness of the gas pedal. By doing so, the dynamics of the gas pedal are changed depending on the changes detected in the safe-field-of-travel. In both approaches, an electrical actuator provides the additional force or stiffness. The main hypothesis of this dissertation is the assumption that with the appropriate haptic feedback of longitudinal traffic information drivers will adopt a force-task in controlling the haptic gas pedal. Experimental verification leads to the conclusion that the stiffness feedback design with time-to-contact information scaled by time headway performs best in this respect.