MICROSCOPIC SIMULATION OF ROAD TRAFFIC Laurent BREHERET, Managing Director SODIT 2, avenue Edouard Belin – 31400 Toulouse – France Phone : +33 562 17 58 01 – Fax : +33 562 17 57 91 – Mail : [email protected]

SUMMARY Road traffic simulation has been developed these last years. It is more and more used by traffic operators and it is an efficient tool to analyse a large range of problems related to traffic conditions which can not be studied by analytic methods. SODIT company has developed its activities in traffic simulation by using the SITRA software and has achieved numerous studies related to traffic conditions and road planning with this tool. This software enables to modelise any type of vehicles on road and urban networks in a realistic environment. It particularly fits to assess urban traffic control strategies, bus priority or guidance or information strategies.

MAIN FEATURES OF THE MODEL DESCRIPTION OF THE NETWORK There are two levels to describe a network in SITRA. First a « macroscopic » vision made of nodes and links where a node can be a crossroad, an input node or an output node. Then there is a « microscopic » level where rules of vehicle driving are defined, made of connection points or lanes. The Figure 2 shows an example of two interconnected roundabouts (R1 and R2). On the scheme, two types of lanes are distinguished : lanes inside the intersection which are used to point out turning movements (in blue colour) and the connection lanes which belong to the links. This modelisation principle enables to represent any type of roundabout. [Gabard, 1998].

CAR FOLLOWING LAW AND VEHICLE BEHAVIOUR Different categories of vehicles can be modelised by SITRA (cars, trucks, taxis, tramways, bus …). On one hand, they differ by their geometric and cinematic description and on the other hand by their level of equipment (on-board information, guidance system). It is relevant to point out that SITRA is an open model which enables the users to add their own models of vehicles.

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Voie appartenant à un chaînon

Point de conflit

1 chaînon

Point de connexion

Voie appartenant à une intersection

Figure 2 : Modelisation of two connected roundabouts

Figure 1 : Modelisation of a simple crossroad

TRAFFIC LIGHT CONTROL AND INFORMATION SYSTEMS Because of its design, SITRA achieves first the simulation of vehicle-driver entities and any control strategy (traffic light control, bus control, information system) has to be considered as an external system of the simulation tool. Thus, any external programme developed by a user can have effects directly on the simulation process. A simple data exchange protocol between the simulation model and the external strategy enables the synchronisation of the software. Anyway, to make the task easier for the users, the most simple strategies (such as fixed time traffic plans) are directly integrated in SITRA. Example software

of

an

external

A specific external software has been developed to process traffic light control. This tool enables to create traffic light plans, to follow the real-time control with the possibility of adjusting in real-time the simulation process. The main advantage of this software is to implement easily bus and micro-control strategies : skipped phases and green extensions, in the respect of safety rules (matrix of clearing times) of crossroads controllers. It can be naturally interfaced with the simulation process, by gathering counting data from measurement control centres and by managing traffic light controlled by SITRA.

Figure 3 : Traffic control strategy

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POSSIBILITIES OF MODELISATION Express ways and motorways with their ramp metering Legal traffic signals : traffic lights, roadsigns and information signs Traffic mearusement centres or communication beacons Incidents, bus stops and parkings Reserved lanes : TCSP, slow vehicles Articulated vehicles : tramways, trucks Pedestrian lanes

SITRA OPERATION SITRA can : Assess guidance and information strategies Validate and optimise a project, Analyse the control of an axis, Assess the operation of reserved lanes to buses or tramways, Assess the impact of a road infrastructure, Control in real time conditions the traffic light strategies and more particularly the bus priority strategies.

THE DISPLAY OF RESULTS SITRA puts forward a real 3D environment, by being compatible with previous versions. The possibilities of using this 3D display are numerous : vehicle movements in a environment, flying over a vehicle, on-board display in a vehicle, recording of films, public presentations, …

Figure 4 : 2D display of a crossroad on a road

Figure 5 : 3D display of the same crossroad

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Figure 6 : aerial display of traffic

Figure 7 : On-board display in a vehicle

THE IMPACT ASSESSMENT OF A ROAD INFRASTRUCTURE During this study, it was modelled the impact on traffic of the development of crossroads at the interchange between the motorway A86 and the national road RN13. The simulation was achieved during peak hours with a projection to 2005. This microscopic simulation has underlined the risks of jamming the intersection, because of a very short stocking lane. An alternative was put forward to the project managers, by adapting traffic light plans, so as to avoid this jam.

THE IMPACT ASSESSMENT OF BUS PRIORITY STRATEGIES In the frame of the traffic control strategy by itinerary implemented in the Val d’Oise department, an experimentation of a new system taking into accournt buses at crossroads has been carried out. Preliminary tests have been achieved on the city of Bessancourt, by applying a control strategy validated prior to simulation. In the study and tests which have followed on this site, two crossroads have been developed, and all buses are equipped. All the results have been positive, the bus priority system will be extended to the whole department..

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CONCLUSION For several years, simulation tools have been more and more used to achieve traffic studies. Project managers do no longer hesitate to implement these tools, when they have to choose among several solutions or to validate a road planning project. One has to recognize that the cost of such a study achieved before beginning the project is not significant as compared with gains it can generate. Indeed, in such complex projects, simulation is a necessary tool which can enable to better control risks related to a project, a theoretical analysis can not take into account all the calculation parameters. Simulation can also enable to better display the impact of a project : a 3D display is clear and explicit. The well-controlled displays can then be a good support for discussion for decision makers, even in phases of public concertation. At last, one must not hesitate to call for experts with high know-how and experience in simulation, this can be a guarantee of reliable results ; indeed it is always interesting to gather statistical data coming from simulation with more qualitative indicators, for example in a multi-criteria analysis.

REFERENCES Gabard J-F (1991). Car-Following Models. Concise Encyclopedia of Traffic and Transportation Systems, M. Papageorgiou (Ed. Pergamon Press), Oxford. Gabard J-F, Breheret L (1998). The SITRA-B+ Microscopic Traffic Simulation Model Examples of Use and Future Developments. Informs Meeting, Montreal, April 1998. Helly W (1961). Simulation of Bottlenecks in Single-lane Traffic Flow. (In Herman R.C. Ed.), Proc. Symp. Theory of Traffic Flow. Elsevier, Amsterdam, pp. 207-238. Magne L, Rabut S, Gabard J-F (2000). Towards an hybrid macro-micro traffic flow simulation model. Informs Meeting, Salt Lake City, 7-10 Mai 2000

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