The invention relates to a method of determining at least one eco-driving indicator wherein at least a first indicator (IND) is determined as an optimal speed (Vopt) that minimizes the energy consumption. Calculation of optimal speed Vopt is constrained by measured instant speeds Vmes at breakpoints of the travel where the driver has to adapt his driving according to conditions external to the travel. Once the eco-driving indicator is determined, it can be displayed (AFF) and/or the vehicle can be controlled (COM) in accordance with the indicator.