One-dimensional unsteady Euler equations are solved for the investigation of the flow field induced by a train entering a tunnel. The effect of the moving train is included in the basic equations as an area change in time. The equations are discretized by the finite difference method, and the calculations are performed for trains with various speeds, cross-sectional areas and nose area gradients. Effects of these parameters on the strength of a compression wave and the maximum pressure gradient are studied. Computed strength of the compression wave shows good agreement with the theoretical 1-D analysis and the axisymmetric numerical simulation. The one-dimensional flow model is validated through the comparison of computed pressure gradient with multidimensional numerical simulations.