For the explanation of these two parameters, information on cold-start extra emissions and on the cold transient phase has to be identified. By processing the experimental exhaust emissions of CO and HC, measured during the UDC EUDC driving cycle with cold-start for the motorcycle B, the cumulative curves of emissions were obtained in function of the time (the choice of this motorcycle was determined by the plentiful amount of data available for this vehicle in order to demonstrate the whole procedure); CO and HC experimental cumulative emissions are displayed in Fig.3. As proposed in a methodology of EMPA (Weilenmann2001) to calculate the coldstart emissions, the contribution of hot emissions on the cumulative curves can be fitted with a line (characterized by high correlation coefficients) whose intercept is considered equal to cold-start extra emissionEC. The duration Treg of the cold transient is calculated as the instant in which the curve of the cumulative emissions diverges from the linear regression and, exactly, cuts the line parallel to the linear regression but with the constant equal to the constant of linear regression—29standard deviation of emissions (Joumard1999).