In the present paper vehicle noise source modelling work carried out within the Acoutrain project is presented. When the noise source system is surrounded by many reflectors, for example a radiating transformer behind roof shrouds, a single monopole with averaged transfer function is suggested to represent the source. For a source with strong directivity placed in an essentially free space, a “box-source” method is recommended to take into account of the source directivity. The total sound power is in this case divided into five independent noise sources which are obtained via standard sound power measurement methods and certain data processing. Experimental verifications are made for several cases in laboratory and in the field. Good correlation between tests and modelling results are obtained for both approaches.