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.
A small group of vehicles travels through uncoordinated signals while their journeys accumulate on a time-distance plot. The identical trip then replays with signal offsets chosen around the expected travel time. In the coordinated case, green periods line up into a moving window that vehicles can follow from one intersection to the next. The growing trajectories make that green wave visible rather than merely naming it. Coordination matters because reducing unnecessary stops can lower delay, fuel use, and stop-and-go disruption. Its benefit depends on travel speed, cycle length, and traffic direction; a setting that favors one group may serve others less well.
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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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.
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