This paper discusses the development of a software-controlled embedded system to evaluate the effect of communication latencies in hardware-in-the-loop simulation of traffic systems. The tool uses the controller interface device (CID) hardware developed for hardware-in-the-loop simulation with modifications made to the firmware to support real-time playback (RTPB). RTPB simulators have been used in power systems as a cheap alternative to real-time simulators. In some cases RTPB is the only possible simulation method. This paper presents the application of RTPB to traffic simulations using actual traffic controller hardware.