Less is More: Improved Traffic Flow Efficiency Effects at Vehicle-Actuated Signalised Intersections with Permitted Conflicts as opposed to Protected Conflicts

Abstract

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.