Underground trains passing below structures may produce vibrations harming occupants and nonstructural elements, though they do not usually result in structural damage. This is a problem of more importance when assessing buildings such as libraries, hospitals, laboratories, museums, etc. To prepare simple tools to fulfill design needs, in this paper assessment spectra for various underground trains moving with different velocities are calculated. Using these spectra, without resorting to the time consuming and costly analysis of a tunnel-soil system under moving loads, the maximum structural responses can be calculated rapidly. To make this end, the soil-tunnel interaction is modeled using a 3D finite difference scheme under the standard moving train loads. The dynamic analysis of such a system results in the ground surface vibration time histories at different distances from the tunnel axis. Then the maximum values of velocity responses are calculated for an SDF dynamical system. The above calculations are accomplished for different train velocities, tunnel depths, distances from tunnel, and soil types, and are presented as assessment velocity spectra.