PROGRAMAÇÃO SEMAFÓRICA: UMA ANÁLISE COMPARATIVA DE ALGUNS MÉTODOS

Porto, Walter · 1994 · DOAJ

DOI: 10.14295/transportes.v2i1.331

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Summary

This paper presents a comparative analysis of various methods for fixed-time traffic signal programming at isolated intersections. The study evaluates methodologies based on two distinct theoretical foundations: those utilizing saturation headway and those utilizing saturation flow. The primary objective is to assess the precision, data requirements, and safety implications of these approaches, with specific attention to how they handle vehicle traffic, inter-green times, and pedestrian crossing needs. The analysis categorizes methods such as Greenshields, Maecke, Gleue, Pavel, Webster, and the Highway Capacity Manual (HCM). The authors compare how these methods calculate effective green times, cycle lengths, and inter-green intervals. A key distinction identified is that saturation headway methods embed influence factors affecting maximum flow into a single measurable value, whereas saturation flow methods require separate determination of these factors. The study also examines the formulas used to determine pedestrian green time, noting that only Webster, HCM, and Maecke provide specific calculations for this parameter, while others like Greenshields, Gleue, and Pavel do not mention it. The findings indicate that methods based on saturation headway, particularly Maecke and Gleue, offer significant advantages in terms of data collection efficiency and safety. Saturation headway can be measured easily in the field by a single technician, reducing the time, cost, and technical expertise required compared to saturation flow methods, which demand exhaustive data surveys. Furthermore, Maecke and Gleue are deemed more precise for calculating inter-green times because they account for conflict points and additional time reflecting actual traffic behavior, rather than relying solely on yellow light duration. Maecke’s method is highlighted for its use of Poisson probability to compensate for traffic volume oscillations, ensuring better service quality. However, the paper notes that using international saturation flow values in local contexts reduces programming efficiency due to mismatched local traffic conditions. A critical conclusion is that all analyzed methods prioritize vehicle flows, relegating pedestrian needs to a secondary status. Pedestrian green time is typically distributed after vehicle cycles are defined, often utilizing "all-red" periods to ensure minimum crossing times without disrupting vehicle flow. While Webster and HCM define minimum pedestrian green times, and Maecke offers a more elaborate formula based on demand and walking speed, none of the methods integrate pedestrian requirements into the initial calculation of the signal cycle. The authors argue that this exclusion fails to give pedestrians the attention they deserve, suggesting a need for methods that incorporate pedestrian demand more fundamentally into the signal programming process.

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