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Controlling road traffic with model-free control

On the occasion of our next X-Novation Talks on model-free control, we discussed the subject of road traffic control with Thomas Lheureux, head of the Intelligent Mobility unit at the DIRN (Direction Interdépartementale des Routes Nord) and with Michel Fliess and Cédric Join, the two researchers who invented model-free control.

Regulating road traffic through innovation

Within the DIRN, the Intelligent Mobility Unit manages innovative projects concerning traffic management on the roads of the North. Our objective is to try to limit congestion in the Lille area as much as possible. Every day, 5 million trips are made within the European Metropolis of Lille, explains Thomas Lheureux.

To mitigate congestion, traffic control is currently the best solution. Several actions are used to regulate traffic: dynamic speed control through variable message signs, routing, driver information and access control. This last action seems to be the most promising, since it acts on the entry rates of the ramps to maintain the traffic densities on the main road below a certain critical value.

The northern highways use dynamic signs and access control to regulate road traffic. Both systems give us satisfactory results, says Thomas Lheureux.

The ALINEA strategy

Initially, the DIRN experimented the ALINEA strategy on the A25 freeway, an isolated access control tool on urban and suburban freeways. However, it was abandoned in 2015 in favor of model-free control.

Although easy to parameterize, the ALINEA strategy had 2 major problems for the A25. The first was the activation of access control not because of congestion but because of the detection of stop-and-go or emergency braking events. The second was the change in the duration of the green light, which was very abrupt. For these reasons, the DIRN has favored model-free control on the A25 and on other freeways: the A22 and soon the A1.


The usefulness of the model-free control

Model-free control was invented by Michel Fliess and Cédric Join, researchers respectively at the École Polytechnique and the University of Lorraine. Although this theory has many uses in automation, it is its application to road traffic that we will first discuss.

Indeed, model-free control is ideal for regulating highway access and decongesting the road network, especially during rush hours. It provides excellent control via traffic lights on the entry flow of the ramp. This access control can be implemented locally and in isolation or coordinated with other highway ramps simultaneously.

The first intelligent traffic light was put into service on the A25 freeway in August 2015," says Thomas Lheureux. The system is activated during rush hour, usually in the morning between 6:30 and 10 am. The traffic light is controlled dynamically. The model-free control system determines the duration of the green light according to the flow of traffic on the freeway and the occupation of the slip road, so as not to block it. The red light lasts between five and 30 seconds so as not to immobilize users on the ramp for too long while limiting highway congestion.

Since 2015, the implementation of the A25 smart light in addition to dynamic speed control has paid off: on average, users save 6 minutes on their 30-minute travel time between 6:30 a.m. and 10 a.m.

Based on these results, the DIRN has installed the same system on the A22 towards Tourcoing and 3 new access controls should be installed on the A1 between Paris and Lille.

Modelless control has also been used in the automotive industry, for drones, hydroelectric dams (2010 innovation prize awarded by X), greenhouse air-conditioning, wastewater treatment, etc. It is the flagship product of AL.I.E.N. (Algebra for Numerical Identification & Estimation), a start-up associated with X and the University of Lorraine, created by Michel Fliess and Cédric Join. This technology has also been widely used abroad. Let's just mention here smart grids (USA), lasers (USA), exoskeletons (China), batteries (China), ferries (China), artificial tides (Italy), ...


The fight agains traffic jams on the A1 freeway

If travel time is improved on the A25, this is not yet the case on the A1, in the Templemars-Seclin-Vendeville sector. Frequently saturated, the European Metropolis of Lille voted an action plan in December 2019 to decongest the sector. 

 5 measures were adopted to improve road traffic:

→ the creation of a half interchange at Templemars, to connect the A1 freeway and the RM 952 ;

→ dynamic traffic management through access control and variable message signs for dynamic speed limitation;

→ strengthening the network of bicycle routes in the area on both sides of the A1 freeway;

→ modifications to the existing lanes at the Seclin interchange to make traffic safer and better on the RM 549;

→ the creation of a new section of roadway between the RM 952 and the Seclin-Epinette business park.

One lane of the A1 freeway should also be reserved for carpooling, adds Thomas Lheureux.


X-Novation Talks: Modelless Control

Would you like to learn more about model-free control and its application to road traffic? Innovations in mobility? Then don't miss our X-Novation Talks on the subject, which will take place on Tuesday, June 29 from 12:30 to 14:00 online.

In addition to Thomas Lheureux, head of the Intelligent Mobility Unit at the DIRN, you will have the pleasure of discussing with Michel Fliess, Emeritus Research Director at the CNRS and founder of ALIEN ; Cédric Join, professor at the Centre de Recherche en Automatique de l'Université de Lorraine - CNRS and founder of ALIEN; and Sylvie Tonda-Goldstein, head of partnerships at the Direction de l'Entrepreneuriat et de l'Innovation de l'X, and director of the subsidiary FX-Conseil for the valorization of research results.


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