GSM-R, an international 2G wireless communications standard for railway communication, a part of the European Railway Traffic Management System, is acknowledged as a crucial component of reliable and safe railway operations. GSM-R has a limited lifespan, it becomes obsolete and no longer fulfills the ever-increasing demand for high-speed, high-bandwidth, low-latency applications for railway transport. A successor to GSM-R, FRMCS is the emerging global standard for railway mobile communications, which meets the needs and obligations of rail operators around the world in the era of digitalization. FRMCS is designed to use many modern mobile communication standards, such as LTE, LTE-A, and 5G NR, but the latest decisions of the European Railway Agency and the International Union of Railways show a clear preference for 5G. While the development and deployment of the next generation railway mobile communication system are still in the process, methods for the accessible and accurate investigation of radio coverage conditions for 5G networks should be studied, described, and tested. The paper presents the results of testing, evaluating, and analyzing the radio coverage conditions of 5G cellular mobile communication networks (CMCN) in Latvia. Results of the taken measurements were used to determine the quality of mobile communications and the influence of the environmental factors on the uniformity of cellular network coverage for railway communication.