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.

Permitted conflicts at (vehicle-actuated) signalised intersections are widely researched, though with the main focus on the traffic safety implications, because with permitted conflicts, two or more conflicting streams at a signalised intersection receive green at the same time, and thus meet at the conflict zone, as opposed to protected conflicts. The literature pays little attention to the traffic flow efficiency effects. Although some literature introduce some of these traffic flow efficiency effects, no detailed research has been done. This Additional Graduation Work contributes to this knowledge gap by introducing the potential traffic flow efficiency effects of permitted conflicts. In a simulation study, in which the gap acceptance behaviour of the simulation model Vissim is briefly tested, it is found that permitted conflicts (i) reduce the cycle time, (ii) reduce the queue length, and (iii) reduce the delay experienced by various road users at the signalised intersection. However, this comes at the cost of reduced saturation flow. Also, it is hypothesised that there is some turning point in terms of traffic flow volumes, and the distribution of volumes per approach at which the traffic flow efficiency effects become negative. This relates to the various traffic safety conditions that must be met at the signalised intersection with permitted conflicts as well, to ensure a safe conflict handling, which include that the traffic flow volumes may not be too large. Nonetheless, the traffic flow efficiency effects, in terms of intersection throughput and capacity, queues, and travel times and delays, of implementing permitted conflicts, as opposed to implementing protected conflicts on signalised intersections, are positive, in that sense that it resulted in shorter cycle times, less delay, and shorter queues on average. For signal groups with priority, the number of stops also decreased. Although there is a risk of oversaturation, the overall conclusion is that the traffic flow inefficiency effects are positive on average. In short, this comes down to that fewer protected conflicts, equals a higher traffic safety risk, but also a more efficient traffic flow, on average, hence the title of this research.