The development of future railway systems is contingent on the evolution of wireless communications technologies and their ability to serve more sophisticated use cases. Recent proposals to extend the 3rd Generation Partnership Project (3GPP) 4G or 5G standard for use in next-generation railway wireless communications presents a problem in that they are still based on Orthogonal Frequency Division Multiplexing (OFDM), which is vulnerable to Doppler-related effects when traveling at high speed. Orthogonal Time Frequency Space (OTFS) is a promising new modulation technique that can handle communication even in very high vehicle speed cases. In this paper, we investigate the performance of OTFS in terms of achievable rate under different High Speed Rail (HSR) environments, while taking into account the impact of practical but non-biorthogonal pulse shapes. Simulation results show that OTFS provides consistently high achievable rates regardless of the environment, and that the rates are relatively insensitive to the speed of travel.