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A portable emission measurement system (PEMS) was used to measure the real-world driving emissions pertaining to a Japanese middle-sized heavy-duty vehicle. The testing was performed with the vehicle being driven in the metropolitan area of Tokyo in four seasons (January, June, August, and November) to analyze the seasonal dependence of NOx and CO2 emissioans. The experimental results indicated that the amount of NOx emissions was particularly high in the cold season, owing to the slow starting of the NOx detoxification systems, that is, the exhaust gas recirculation and urea-selective-catalytic-reduction systems, under low ambient temperature conditions. In the real-world driving, a high acceleration pattern was observed in the low-speed region, which is not considered in the world harmonized vehicle cycle, which is the worldwide official driving mode in the chassis dynamometer experiment. Finally, the transient emission tables for NOx and CO2 were constructed based on the PEMS measurement results and the classical mechanic theory. The constructed tables well replicated the experimental results in all the considered conditions involving different ambient temperatures and locations. The proposed approach can be used to evaluate emission inventories in the future. [ABSTRACT FROM AUTHOR]