French traffic noise prediction models are based on vehicle noise emission values defined by the "Guide du Bruit des Transports Terrestres", issued in 1980. A research programme was established in order to update these values and take into account developments in car and road technology. The methodology followed to output emission values has been developed by successive steps, as the processing performed on the collected data went along. After several attempts the shape adopted for the emission formulas considers the vehicle pass-by LAmax as the sum of two subsource contributions: the power unit contribution which varies with acceleration and the road gradient, and the tyre/road contribution which varies with speed and the road surface type. New emission values are now completely defined, and ready to be used in noise prediction models.