To evaluate traffic signal controllers, and vehicle-actuated traffic signal controllers in particular, in terms of how they are performing with respect to the road authority’s policies on traffic flow and accessibility, traffic safety, and environmental factors, several methods are developed in practice. However, in scientific literature, little attention is paid to this type of traffic signal controller evaluations. Indeed, it is found that a functional, and integral evaluation and diagnosis method for traffic signal controllers, based on a multi-variable assessment, is currently lacking. This thesis tries to fill this gap, by developing, and presenting an integral method, which detects inefficiencies in terms of traffic performance functioning, scores the vehicle-actuated traffic signal controller, diagnoses the cause of the detected inefficiency, and propose countermeasures to improve the traffic performance functioning of the vehicle-actuated traffic signal controller, based on a multi-variable assessment. This resulted in a five-step procedure, in which consecutively (1) the multi-variable performance indicators are selected, (2) the computational models are calibrated, (3) inefficiencies are detected, (4) the problems are diagnosed that caused the inefficient performance, and (5) optimises the traffic signal controller by implementing the countermeasures that aim at mitigating the diagnosed problems. The procedure includes a feedback loop to check whether the proposed countermeasures were effective. The testing of the method in a case study, using simulation data, showed that the method is indeed able to successfully detect inefficiencies, and diagnose the corresponding problems. Although the presented method is not perfect yet, its potential is clear. Therefore, it is recommended to develop the method further in the future, and include the use of data from practice as a way to make the method more widely applicable.