In order to provide a significant proof of validation of this procedure, in Table3for the two pollutants the similarity is apparent between these cold emission factors (ecold * ) and those obtained (ecold=EC/Treg) through the analysis of the experimental cumulative emissions exposed in Fig.3. Moreover, it is evident that the cold emission factorecold * , as calculated in (6), is function only of f0, and so it is independent from the specific driving cycle; this consideration involves the additional conclusion whereby, for a particular vehicle and pollutant, the experimental results of an individual driving cycle are satisfactory for the estimation of the cold emission factorecold * . In this context, the CO and HC cold-start emissions (EC) of motorcycle B, available from Table3, were estimated for each driving cycle against the pertinent cold transient durations (Treg ) and are shown in Fig. 5; these value pairs (EC; Treg) have a linear interpolation characterized by an acceptable degree of approximation, and the slope of these lines is exactly the cold-start emission factors concerning the specific vehicle and pollutant in examination. The hot emission factorsehotof all considered driving cycles, also exhibited in Table3, were calculated by the slopes of the linear regression of the experimental cumulative curves of emissions, already shown in Fig.3.