We are developing a three-dimensional simulation tool for wave field induced by running trains in the wayside, in order to support design of measures to reduce the vibrations for environmental preservation. This paper shows some remarks on source modeling in the simulation, which may be important independently of numerical schemes of simulation. If excitation loads are modeled as ones driven with synchronization with vehicle arrival and a propagating system is homogeneous, responses are found out negligibly small in far field. Realistic responses are obtained by assuming vibratory loads that are not synchronized with vehicle arrival. However, it is not a unique model to obtain realistic responses. If the propagating system is inhomogeneous near the moving route, realistic responses are generated even by assuming the vehicle-synchronized loads. In addition, if the vehicle-synchronized loads are modeled with a finite length of the route, responses show realistic amplitudes even in a homogeneous propagating system. They are, however, simply contributions due to waves induced by loads suddenly risen up at starting and ending points of the route, not ones to be expected. The contributions might lead to a serious misunderstanding of the numerical result, since the effect is not easily identified particularly in a frequency-domain simulation.
