Adresse:

Cité Descartes, Champs sur Marne
77447, Cedex, France.

Accès:

Ifsttar Batiment Bienvenüe
Ecole des Ponts ParisTech (ENPC)

Organisateurs:

N. Farhi, N. Bhouri et J-P. Lebacque (Grettia).
Z. Christoforou et F. Leurent (Lvmt).

Contact:

nadir.farhi(at)ifsttar.fr
+331 81 66 87 04

Session prochaine

Date: 19 Juin 2017
Lieu: Ifsttar - Salles B017-B020 - 14 - 20 Boulevard Newton - Marne-la-Vallée, France. Accès .

Programme:

14h00 Guilhem Mariotte, Ifsttar/Cosys/Licit. Slides
Titre. Modeling traffic flow at the network scale with multi-reservoir systems using the MFD.
Résumé. Over the past decade, the Macroscopic Fundamental Diagram (MFD), relating the mean flow vs the mean density of a given urban area, has appeared to be a powerful tool to describe traffic states at the network level with few implementation and computational efforts. Many studies (e.g. Knoop & Hoogendoorn, 2014, Yildirimoglu & Geroliminis, 2014, Yildirimoglu et al., 2015, Haddad, 2015) have notably used MFD-based traffic simulators for several applications, like traffic state estimation, perimeter control or assessing routing strategies at a large scale. Their modeling approaches take advantage of the multi-reservoir representation of a city, where the dynamics of each urban subregion is described by the single reservoir model of Daganzo (2007). This framework, also referred as the "accumulation-based model", assumes that the reservoir outflow is proportional to the circulating flow inside the zone. However, while being acceptable in slow-varying conditions, this hypothesis may be too restrictive when the demand evolves too fast as shown by Mariotte et al. (2017). An idea, initially proposed in Arnott (2013), has been exploited in Daganzo & Lehe (2015) and then Lamotte & Geroliminis (2016) to design a "trip-based" formulation of the MFD model. This approach considers that all users travel at the same speed at a given time, and exit the zone once they have completed their individually assigned trip length. Although both approaches have already been used many times in various studies, challenging issues about congestion propagation between the reservoirs have received little attention in the literature. This presentation intends to shed some light on these questions, together with a short overview on these models. Case studies of reservoirs crossed by routes with different lengths will be presented.
   
14h45 Cyril Nguyen Van Phu, Ifsttar/Cosys/Grettia. Slides
Titre. A vehicle-to-infrastructure communication based algorithm for urban traffic control.
Résumé. We present a new algorithm for urban traffic light control with mixed traffic (communicating and non communicating vehicles) and mixed infrastructure (equipped and unequipped junctions). We call equipped junction here a junction with a traffic light signal (TLS) controlled by a road side unit (RSU). On such a junction, the RSU manifests its connectedness to equipped vehicles by broadcasting its communication address and geographical coordinates. The RSU builds a map of connected vehicles approaching and leaving the junction. The algorithm allows the RSU to select a traffic phase, based on the built map. The selected traffic phase is applied by the TLS; and both equipped and unequipped vehicles must respect it. The traffic management is in feedback on the traffic demand of communicating vehicles. We simulated the vehicular traffic as well as the communications. The two simulations are combined in a closed loop with visualization and monitoring interfaces. Several indicators on vehicular traffic (mean travel time, ended vehicles) and IEEE 802.11p communication performances (end-to-end delay, output rate, throughput, and packet error delivery ratio) are derived and illustrated in three dimension maps. We then extended the traffic control to a urban road network where we also varied the number of equipped junctions. Other indicators are shown for road traffic in the case of a road network control where high gains are experienced in the simulation results.
   
15h30 Pause Café.
   
15h45 Kwami Sossoe, Ifsttar/Cosys/Grettia. Slides
Titre. Reactive Dynamic Assignment in Discrete-continuous Large-scale Transport networks.
Résumé. In the field of traffic flow modeling of large-scale surface networks, a bi-dimensional traffic flow modeling framework emerged. It is a family model developed at a greater scale. The theory of traffic flow at this scale of modeling is a high-level of aggregation of road sections and road intersections, in zones of two dimensions. The corresponding network domain of such surface network is approached as a continuous network that comprises infinite secondary roads. A specific dynamic network loading is proposed to compute vehicles flow on such continuous network, while a reactive assignment scheme is designed for dynamic traffic assignment. A Dijkstra-based algorithm is used to find time dependent shortest paths over large networks in this context, where instantaneous travel times are considered instead. Since urban network may comprise major roads like highways, a coupling of GSOM macroscopic flow model (applied to discrete network) with the bi-dimensional flow model (applied to the continuous network) is discussed. The new proposed transport model has the capability of reducing significantly computational complexity. Moreover, the model is suitable for networks with few traffic data sources.