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Projekt Druckansicht

Zyklisches, zeitexpandiertes Optimierungsmodell für Lichtsignalanlagen; Interaktionen zwischen Lichtsignalsteuerung und Nachfrage, irreguläre Verkehrssituationen

Fachliche Zuordnung Verkehrs- und Transportsysteme, Intelligenter und automatisierter Verkehr
Förderung Förderung von 2013 bis 2018
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 223719378
 
Erstellungsjahr 2019

Zusammenfassung der Projektergebnisse

Signal control for urban traffic is an important topic of practical interest. Being able to explicitly model queue built-up at red signals, with the cyclic construction of the time-expanded network, is a break-through of mathematical modeling capabilities. It was shown in this project that the approach can be extended from phase optimization of fixed-time signal plans to the more important green split optimization. An alternative approach are actuated or adaptive signals. As expected they perform worse than fixed time signals in Braess-like situations, where the fixed-time traffic signals can move the routing from Nash equilibrium to system optimum, which is clearly not possible for an actuated or adaptive signal that follows the traffic. We found this not much (if at all) an issue in other practical situations that we investigated. Actuated or adaptive signals also do not depend as much on details of the demand or the intersection geometry. Finally, they provide additional gains when traffic flows fluctuate slightly. Overall, actuated and adaptive signals fared better than initially expected. Robustness was an issue throughout the project. Signal plans might promise much better performance from the mathematical optimization than what they showed in the simulation. For example, the mathematical approach tends to switch signals immediately back to red after the demand has been served, which for any stochastic simulation or real-world situation has the consequence that, because of fluctuations, some vehicle will be stranded at that red light which might have remained green. Without a meaningful extension of these green times, using simulation to evaluate the mathematically found signal plans often displays performances that are far worse than what the mathematical algorithm promised. The project documents several such issues that seem like small differences but lead to large differences in the performance evaluations. By increasing the level of detail in traffic signal modeling (adapting green split, phase order, etc.) the travel time difference between analytical model and simulation increased. This surprising outcome shows that the difference between user equilibria and optimal solutions in the CTEN is not fully understood and calls for further research in the following direction: Which part of the difference between analytical model and simulation is due to the difference between system optimum and user equilibrium, which part results from possibly different equilibria in the dynamic network with traffic signals, and which part is caused by a lack of robustness of the analytical solutions with their sharply timed switching times. Re-routing is rarely considered in the context of signals optimization, but has a strong effect: Gains from optimized signals in urban centers will lead to additional traffic through the urban core, thus worsening environmental impacts. Overall, this implies that signal control schemes need to be evaluated in context, with a large scale model that includes re-routing (and optimally mode and departure time choice), and is able to calculate environmental impacts.

Projektbezogene Publikationen (Auswahl)

 
 

Zusatzinformationen

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