One cost effective solution for traffic control and signaling of monorails and metro rail transit is a communication based train control system (CBTC). Radio transmission is one of the most effective CBTC subsystems. It can increase transportation capacity by moving a block control method with less trackside equipment. This paper discusses the development of a radio propagation simulator for CBTC systems (RAPS). The purpose of RAPS is to calculate the radio-electric signal power and coverage along the track; and consider track configuration, tunnel geometry and obstacles in order to arrange a proper layout of trackside base stations and their antennas. The paper presents a graphical user interface, key technical features, and a case study involving the simulator.