Starting from the 1980s (diesel-engined) vehicles have been tested for exhaust emissions, prior to type approval, using sophisticated standardized transient tests (Transient Cycles). These are usually characterized by long duration consisting of both speed and load changes under varying operating schedules. In the present work, a fast and, relatively, easy to apply approach was developed in order to be able to make a first approximation of the engine performance and emissions during a speed/torque vs time Transient Cycle. The procedure is based on a previous steady-state experimental investigation of the engine for the formulation of polynomial expressions of all interesting engine properties with respect to engine speed and torque. Correction coefficients are then applied, based on experiments conducted on the engine under study, to account for transient discrepancies. Using the developed algorithm, a comparative study was conducted for the European, American and the Worldwide heavy-duty Transient Cycles. It was revealed for the current engine that the European ETC, being the most aggressive and having the shortest idling period, is also the most demanding in terms of absolute emissions (g), particularly soot. At the same time, the importance of abrupt transients (primarily experienced during urban driving) on engine emissions was highlighted. A comparative analysis was also performed that detailed the individual technical and transient characteristics of each cycle. Copyright (C) 2009 John Wiley & Sons, Ltd.