Abstract: Low fuel consumption is very important for a heavy truck. The best combination of engine, gearbox, central gear and tire dimension varies depending on transport task and road conditions. For these reasons it is important to find the best combination of powertrain components so that the optimum operational area of the engine can be used as much as possible. The differences between different combinations are usually very small so it is necessary to drive long distances to ensure a certain difference. This makes the problem suitable for computer simulations. A computer program to simulate fuel consumption and emissions for heavy trucks in long haulage has been created, using the object-oriented software DYMOLA. It has a longitudinal vehicle model and an engine model based on steady-state measurements. To control the simulations a special graphical user interface (GUI) is built in MATLAB. The GUI is used both as a preprocessor, for specifying vehicle and road, and as a postprocessor to evaluate and display results. Simulations are performed on recordings of real roads. In the program it is possible to simulate the whole production range of engines, gearboxes, tire dimensions and so on. Copyright © 2001 IFAC