Traffic Signal Setting at Urban Junctions and Fundamental Diagram: A Before–After Study

The paper analyses the effects of modifying traffic light regulations at urban road junctions, focussing on the ratio between green time and cycle time, as a function of vehicular traffic variables (flows, density and speed) on the links. The analyses are conducted in an urban setting using a before-and-after approach, employing traffic data detected by loop detectors and traffic light control parameters (the ratio between green time and cycle time) that were actually implemented. The data pertain to a central street in the city of Santander (Spain), collected during several significant weeks in different periods corresponding to varying demands for mobility. In the context of existing studies on the flow-density diagram, a function is estimated that considers the ratio between green time and cycle time as the independent variable and link capacity as the dependent variable. The analysis at the link level may be extended in the future to the network level by incorporating the network fundamental diagram into the traffic signal setting design problem.