The speed with which the vehicle fleet is increasing gives the transport sector responsibility for 30% of the emissions generated by all sectors such as the industrial, food, etc., for this reason it is of great interest to quantify the impact of vehicles for assess in a better way the actions to be undertaken in order to mitigate the damage generated. This study seeks to propose a new method for predicting fuel consumption and emissions of Carbon Monoxide, Hydrocarbons and Nitrogen Oxides generated by a vehicle under normal working conditions. Method a uses the value of the instantaneous vehicle specific power and the calculation of the average of the accumulated power of the last few seconds.