This paper focuses on answering the question of how to increase energy efficiency of moving vehicles (i.e. reduce fuel consumption and GHG emissions, particularly CO2) depending on the route they present. The result is the design, development and performance evaluation of Optimal Speed Advisory (OSA) application. OSA optimizes fuel usage and reduces greenhouse gas emissions of vehicles by informing the vehicle of the optimal speed while following a route. It combines the advantages of Vehicular Ad hoc Networks (VANETs) related with portability and scalability in order to reduce carbon dioxide emissions and fuel consumption. Performance evaluation of OSA was performed by analyzing fuel usage, Carbon dioxide emissions, packet loss, and packet error rate in a small number of nodes in a series of simulations. The simulations used software package SUMO to control vehicular traffic flow, and software OMNeT++ as a platform of data implementation, and framework Vehicles in Network Simulation (Veins) as a simulation frame to integrate SUMO and OMNeT++.