For future railway wireless communication networks, it is an effective way to adopt higher frequency spectra with broader bandwidth to enhance the transmission capacity. Nevertheless, massive beamforming techniques are needed to overcome the severe path loss of higher frequency spectra. For railway systems with dual on-vehicle receivers, dual-beam transmissions can be implemented to improve the capacity. The analysis results show that the optimization of dual-beam transmissions depends on the train position. Based on the above, an adaptive beam splitting or integrating communication scheme is proposed. When the train is far away from the base station, to avoid the inter-beam interference, an integrated beam with wider beamwidth is used to cover the two receivers to realize diversity receiving. As the train is approaching the center of the base station, two beams are generated to realize space multiplexing, to improve the transmission capacity and reliability. Numerical simulation results demonstrate that the proposed scheme can adapt to train positions and improve the transmission performance.