A green signal should help clear a queue, but sending vehicles into a full downstream road can simply move congestion into the next junction. Max-pressure control considers both sides of an intersection: the vehicles waiting to enter a movement and the space or queue conditions where they would emerge.
At each decision point, traffic freezes while the four candidate phases and their relative pressures are examined. The phase with the strongest positive opportunity is selected and motion resumes. One decision produces no green at all because every candidate pressure is negative, making the all-red option part of the logic rather than an error. The scene includes nearby junctions so spillback and downstream conditions remain visible. The insight is that an intersection should not be optimized as a standalone queue. Its best immediate action depends on how releasing vehicles will affect the surrounding network.
Four green lights along a corridor do not guarantee a smooth trip. If their timing is unrelated to travel between intersections, a vehicle released by one signal may arrive at the next just as it turns red. The same road can therefore produce repeated stops without any change in demand or geometry.
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An intersection contains several traffic streams that would like to move at the same time. The problem of signal phase design is to allow compatible streams together while separating movements whose paths cross. The video turns that spatial safety rule into a graph problem.
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The center of a conventional intersection forces many turning paths to compete for the same space. A knotted intersection rearranges those paths and schedules passage through several smaller conflict areas, allowing movements to weave through a compact geometry in a controlled rhythm.
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