With the aim of a perfect source model to simulate railway traffic noise within a shorter computational time, this paper compares coherent line, incoherent point and incoherent line sources on the performance of barriers by using an analytical solution, a 2.5-D BEM method and scale modelling tests. The comparison between the analytical solutions and the 2.5-D BEM prediction results shows that the BEM calculations for a coherent line source can be used to approximately show the barrier attenuation spectrum for a one-point source and the single-number rating for an incoherent line source when the barrier is straight on the ground. Then, validations with scale modelling tests were performed outdoors under controlled conditions. The results obtained by using several loudspeakers radiating incoherent sounds simultaneously show good agreement with the 2.5-D BEM prediction results for the one-point source and incoherent point sources, not only for a simple barrier on the ground but also for a double-straight barrier on a viaduct. Based on these agreements, the frequency and longitudinal distance dependences on the barrier attenuation for incoherent point sources are discussed to understand the barrier attenuation spectrum for the incoherent line source.