Research sponsored by the Texas A&M University ITS Research Center of Excellence was used to analyze the application of hardware-in-the-loop simulation at a diamond interchange. The study shows that hardware-in-the-loop simulation can improve the accuracy of traffic operations analysis by removing the inherent differences between emulated controllers and the actual hardware. In this study, a controller enhancement called conditional service was considered for implementation at an actuated diamond interchange. An evaluation of the traffic operations at the diamond interchange was completed using PASSER III-98, CORSIM, and hardware-in-the-loop simulation. The results of these analyses were compared to field observations that were used as the basis for evaluating the accuracy of each of these methods. An assessment of each method was discussed to identify issues and results using each method. One of the important supplementary benefits of hardware-in-the-loop simulation is that it allows engineers and technicians to test signal control strategies and hardware before deployment in the field. This capability provides a platform for innovation and the development of new control strategies. Hardware-in-the-loop simulation is also a valuable training tool.