Use Case Description of VPAIR: Virtual Police Agents for Traffic Guidance

Arturo Gomez, Gladys Diaz, Khaled Boussetta and Nadjib Achir L2TI - Institut Galilee - University Paris 13

99 Avenue J-B Clement, 93430 Villetaneuse, France Emails:{arturo.gomez.gladys.diaz.khaled.boussetta.nadjib.achir}@univ-paris13.fr

Abstract-Nowadays the traffic systems for the transportation of goods and persons is an important subject that affects our economies, social interactions and almost every aspect of our life. Delays and traffic bottlenecks represent a significant inconvenient and problematic in this area. The ITS architectures provides innovative solutions to solve many aspect of this problematic. However these solutions tend to be heavy in infrastructure and costly in implementation and maintenance. Our approach is oriented to traffic guidance systems with light infrastructure and affordable cost to be implemented over urban networks where budget is a vital constraint such as rural areas and developing countries. We present in this paper the typical use case of our solution for traffic routing services. We call our general architecture VPAIR (Virtual Police Agent for ITS Traffic Routing). The objective pursued is to affect the driver decision in such a way as to maintain a fairness System-Optimal.

I. INTRODUCTION

The constant development of our economies and our con­tinuous demand for mobility tend to clog existent traffic networks when many drivers converge simultaneously in the routes. Side effects of traffic bottlenecks are congestion, pollution, delays and indirect economic loss incurred with inefficient transportation systems. For solving this problem there exist several typical approaches. For example: limiting the admission number of vehicles or expanding the number of transportation roads. However a more objective approach is the use of intelligent management in current traffic systems.

The Intelligent Traffic System (ITS) technologies are a good example in solutions for improving traffic management. ITS infrastructures offer wide options for many situations that suffer from traffic congestion and undesirable side effects such as noise and pollution. These kinds of solutions are based on the dissemination of advanced traffic information systems (ATIS) through variable message systems (VMS) and the broadcasting of traffic message channels (TMC). Methods for advanced traffic management systems (ATMS) use active actuators like traffic lights programming to affect the traffic regulation.

However, arguably caveats for ITS solutions are that require costly implementations and not are always affordable to many environments with budget restriction. Our motivation comes from searching ITS architectures for traffic management that are reachable and affordable to traffic networks with funds restriction like rural areas or cites in developing countries.

An important element in traffic management is the auxiliary figure of the police agent. An example of the Police agent

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chore consists to assist regular drivers to reach their next destination. An agent can provide handy information to users based on its privileged knowledge of local traffic surroundings. Traffic agents are useful for managing and avoiding traffic bottlenecks while keeping a secure traffic level. This figure is a complementary aid in managing traffic and that can be exploited for route planning assistance. However this useful agent is not available all time (24/7) and the number of staff presence on the streets is limited.

We inspire our proposal based on this role with the system of Virtual Police Agent (VPA) for traffic guidance services. Our system is inspired on the role of real police agents where their services are highly demanded. This system does not intend to replace a real police authority. But is rather a complementary assistant to police forces with the aim to improve vehicular traffic fluidness. The VPA will be located in transited areas where drivers will demand assistance for route planning. The VPA coverage is a well defined sector. The VPA provides route plan assistance from the sector in charge. The following VPAs on the drivers' way will be able to provide further directions to arrive at the final destination.

For the reminder of this document we present the use case description of our proposition with the development of the main idea. The section two present the related work. In section three the user case description is presented. The fourth section presents the conclusions and related work.

II. REL ATED WORK

A. Intelligent Traffic System

Traffic management and traffic control systems have seen early implementations in systems like SCOOT, UTOPIA, OPAC, SCATS, PRODYN [1], [2], [3], [4], [5]. These im­plementations propose hierarchical approaches, analytical de­signs and algorithms for real-time applications. However these systems suffer when encounter difficult conditions in traffic congestion.

Traffic guidance systems are regular services on roads provided with ITS infrastructure equipment. Traffic data in­formation is collected from traffic sensors deployed along the road that detect the traffic density, speed and travel time parameters. The information collected is usually sent to a central facility for its processing. The data is then transmitted back to the drivers via VMS panels and radio broadcast to onboard GPS systems with TMC enabled. The Vehicle

Information and Communication System (VICS) implemented in Japan more than a decade ago, provides navigation services and assistance for safe driving [6]. This ITS infrastructure is based on a deployed array of sensors reporting to a central server and then transmitted to users via the mentioned methods of dissemination. The VICS system provides a proprietary GPS device able to receive the updated information with the objective to recalculate the driver route plan.

Also GPS manufactures with a large base of installed units retrieve traffic statistics anonymously from active GPS. Gath­ering real traffic patterns information from drivers' navigation permit to update their network with time-varying parameters. This information is collected to a central server and sent to users' GPS to recalculate route plans with updated informa­tion. Compared to regular GPS system where the route plan is selected from static database this new approach delivers an interesting advantage from traditional navigation system.

Actual ITS systems provide advantages that increment our chances to reach our destination rapidly. However some caveats can be signalled from the anterior solutions. These so­lutions are based on User-Equilibrium (UE) [7]. This perspec­tive is biased to the user benefit where every driver chooses its own route plan according to its own cost. Even though this is a typical approach for many guide transportation system this is not an optimal way as it may appears. Roughgarden [8] quantify this phenomenon of unfairness with experimental results where the System-Optimal (SO) minimizes the total latency in comparison with UE, the last incurred in a larger global latency. Also, the generic traffic information transmitted indistinctly to a general public may produce adverse traffic pat­terns. That is, many drivers following the same lead reported for the traffic routing system may produce jams where are not supposed to happen. Therefore a requirement for further coordination is missing and new approaches to global organi­zation should be implemented to achieve an effective traffic system harmony. On the other side these ITS infrastructures are heavily supported with hardware and information systems. The cost for deployment and maintenance tend to be costly. The access to this type of well established technologies are not always reachable for all urban environments with budget constraints.

B. Multi-Agents Systems in Transportation Systems

Intelligent transportation is also studied from the perspective of agents. An agent is an autonomy entity capable of taking local decisions and creating collective smart behaviours while collaborating with other entities. Entity autonomy is governed for the awareness of its local resources, its environment at its capacity to react in a coherent auto-organization with the purpose to achieve a global objective.

Ever since the apparition of agents concept more than two decades ago, the spread of its use in transportation requires more research to cover the wide spectrum of traffic man­agement. Agents systems are strongly based on hierarchical architectures for organization, coordination and execution of

tasks. Where a global entity is needed to coordinate the agents efforts into a coherent global behaviour [9].

An important niche for traffic management involving agents is active actuation systems (e.g. traffic lights programming) [10], [11], [12], [13], [14], [15]. On these solutions, agents collaborate in better traffic programming to provoke traffic fluidness. This include the traffic data collection on road intersection. Other propositions for traffic management are not based on traffic actuators, but rather rely in influencing the driver decision through traffic information sent to them. And this is the area where we are interested.

Other inclusions of agents in transportation are for example specific applications to detect weather problems conditions for traffic monitoring with reactive actions [16]. The Traffic Agent-City for Knowledge-based (TRACK-R) is a multi-agent application for route plan recommendation between cities, taking into account the route travel time parameter [17]. In [18] the agent-based for traffic detection and management system use stationary and mobile agents for collection of traffic data in more like a traditional ITS infrastructure model. In [19] authors provide experiences using agent-based architectures for traffic management, using centralized and decentralized agents for detecting congestion and alleviating the problem through ITS traffic actuators.

Our own approach utilizes main ITS features, hierarchical architecture of central and distributed agents. Our perspective is also a special purpose applications oriented to provide guidance services to regular drivers while promoting a com­mon transportation cost. In System-Optimal traffic schemata, fairness is a user constraint to be resolved. We assume that drivers are not willing to sacrifice their own travel time for the interest of the majority. Hence a fairness based on user constraints is intended to be implemented to dodge inequalities of granting special priority to some users to the detriment of others [20].

c. lve closing the loop

Inter-vehicular communication (IVC) is a promising evo­lution for transportation system. Actual ITS infrastructure disseminates data to in-vehicle systems in one direction. The chain of information is symbolically broken when the information is terminated at the vehicle and no feedback is sent back. Providing vehicles with the capacity to communicate and report their own navigation parameters will permit to close the cycle of communication. However the actual defies in vehicular communication are well-understood to be not so simple to overcome due to wide geographic distances, fast mobility of nodes and the scarce or heavy density scenarios presented.

Our proposed SO implementation will not be possible without the IVC capabilities. For the next section we present our use case oriented to provide traffic routing guidance under SO bases.

III. USE CASE DESCRIPTION

A. Scenario

Drivers may require constant information before taking per­sonal decisions in route planning matters. Advanced services provided in major cities consist in providing time-varying parameters to onboard GPS users. In this case the personal navigator may be able to avoid reported jams and risky situations attempting against the user travel time. Although this service is considered more accurate is not perfectible because individual actions may incur in unorganized traffic patterns. This happens, for example when the users swarm the alternative route paths without evaluating before the possible consequences of provoking newer clogs.

Our supposition is that better solutions based on auto­organized system with IYC capabilities are capable to emerge into smart traffic behaviours. This is the bottom-line of the most important considerations of our proposition. The base of our proposed service is the traffic guidance as a strong way to influence the driver traffic pattern. This influence can be used as a traffic management instrumented based on coherent and global coordination from the perspective of network flow management.

Our system is intended to be implemented mainly in urban traffic scenarios with poor or complete absence of actual ITS services. We consider that users are able to use our system provided with a regular smartphone device (GPS and Wi­Fi enabled). The implementation of mechanism to assure the anonymity of participants will permit to comply with privacy policies.

Despite the fact that searching routing solutions in large networks tend to be a NP-hard problem. We based our solution in small and manageable sections governed for a VPA able to provide local routing. More agents distributed along the user path will be able to solve the routing problem up the final destination.

B. Architecture VPAIR

The Virtual Police Agent for ITS Traffic Routing (VPAIR) is the name of our architecture proposed [21]. This is essen­tially a specific application service for drivers' guidance. Our System has been intended to be an alternative and affordable traffic system in comparison to actual ITS architectures. The intention is not to replace existent and well established ITS so­lutions but to provide affordable solution for specific markets. We envision two key concepts in our architecture a local and global view. The local view perspective will resolve the traffic routing at a microscopic level for a determined geographic space, this is the VPA sector. If we consider that the sector has a moderate size (some hundred square meters) the entry and exit street points bordering the sector can be defined as the possible combination of internal Origin-Destination (OD) pairs. The idea behind is to fragment our original graph in small sub-graphs (sectors) in order to calculate best path for every interconnected OD pair segment.

The concept of global view comprises the organizational aspect of VPAs in the sense of ordering and assembling the

puzzle of segmented OD pairs to the original end-to-end OD route. The figure 1 depicts the above explanation; here the user requests a route plan for its final destination. The overall path is given by a global entity in terms of a succession of intermediate sectors. Every sector resolves for a fraction of the original OD pair. The definition of involved actors is described below:

• User. This actor is an outsider of the system and is represented as a regular driver demanding a route plan from the system.

• Sensor Traffic. This actor is external to the system and refers to measuring devices of traffic parameters (e.g. loop detector, traffic cameras and vehicles traffic information).

• VPA (Virtual Police Agent). This agent of the system provides local route plan and sector flow management. This can be programmed with directives sent from the global entity of the system.

• PGB (Police Geofiow Broker). This agent of the system represents the global entity that coordinates the works of distributed VPAs. Their duties are related to the assignment of end-to-end route planning of users. This maintain a global network flows that is reported for the VPAs. The coined Geofiow term refers to the traffic flow representation in a geographic space. In practical terms this is a dedicated Geographic Information System for Transportation (GIS-T)[22].

• Police Authority. This human operator is the authority in charge to dictate global traffic policies in order to be enforced in the system.

sectorL•

o o o

GEONETWORK

Virtual Police Agent (VPA)

Fig. I. VPAIR: Virtual Police Agent for ITS Traffic Routing Architecture

C. Use Case

Our Virtual Police Agent proposition is an autonomous en­tity in charge of a geographic sector. The VPA main objective is to provide route plan to regular drivers asking for directions while entering into the coverage area of the VPA.

We define our geographic network area (geonetwork) as the complete universe of our traffic system. The area covered for the VPA is the sector. The definition of a sector is the total area where the VPA is aware of the time-varying traffic conditions parameters. Such traffic data is assumed to be

collected from local sensor traffic devices: local loop detectors, traffic cameras, wireless traffic sensors [23].

The VPA sectors are deployed along the city where their services for routing traffic information can be required. The VPAIR architecture (figure I) shows how every agent provides the route planning up to the destination of the user. Every route plan given is biased to reach the next VPA. The PGB entity coordinates the VPAs efforts in providing the global effect of a System-Optimal. The main processes that describe our architecture are defined in figure 2. The service starts when a driver commences its trip in requesting the initial global route plan. Once the route is fixed the driver will ask for further local route plan at every VPA point until the final destination:

• Global Route plan assignment. Provides users a macro­scopic route plan, this is the path of sectors to hop in.

• Local Route plan Assignment. Provides users a micro­scopic route plan, this is the route plan for navigating inside every sector.

The basic main processes g Global Route-Plan � coordination The Global Route-Plan

� : Rou.te-Plan I

I assistance I

Origin Destination

Fig. 2. Main processes of the VPAIR architecture.

D. The Global Route-Plan process

This process corresponds to the global treatment of a user route plan request represented in diagram 3. We consider that users are in a discovery process searching for the VPA ser­vices. Once the VPA service is detected, the user is identified in sending the solicited OD pair to be calculated. The current VPA intercept the request and forwards it to the PGB to register the user in case this is a new user.

Here the PGB agent provides services of AAA (Authen­tication, Authorization and Accounting) for user registration. After that, the process for the global route plan is delivered to the VPA and up to the user. If the destination is inside in the same sector the VPA is in charge to provide the guideline route. For the former case the PGB retransmit a copy to the concerned VPAs targeted in the global route plan that was delivered to the user.

In general terms the PGB maintains a membership regis­tration of all users tracked with the reports sent by the VPA agents. The PGB holds a holistic view of the active network flows instantiated and reported by every VPA sector. Here the principal service is the global route plan delivery. This route

Sequence interaction for: J The Global Route-Plan

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registered ---- --:S��::'� If local

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---- ------------If External

Destination

Forward(ID_User, Route_Plan)

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(ID_User, ID_VPA)

I Response AAA

10 User,lD VPA, Auth OK)

---------------------Request (lD_User, ID_VPA,

Global Route_Plan)

Response

fID_User,ID_VPA,

Global_Route]lan)

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I I I �istration l I � 1D_user l

_______ J _____ I

_______ J _____ �data a�d �_RoutrPlan

I I

Fo<w"d , I �a

USe"D' (ID_User,ID_VPA, Route Plan Route]lan) � -

Fig, 3, Global Route-Plan process

plan consists in the enlisted number of sectors to jump in, and also the entry and exit points of such sector.

The figure 4 shows the enlisted route plan that consists in the number of sectors to traverse between the original source As to final destination At. And the entryways an exit points for every sector. The local navigation process of segment Ai to Aj is delegated to the local route plan process revised in next subsection.

� � �

Ai C1

Sec\2r .f!l �_..:::S"'e""ct""or'-C::c2=_____' _ ___"S""e",ct""o'_r C",-1,----,

As

Global Route Plan Sector C1 = Ai -> Aj Sector C2 = A'j -> A'j Sector Cn ...

Fig, 4, Global Route-Plan definition

E. The Local Route-Plan process

This process represents the treatment for the local route plan inside of each sector, This is the path that the user must traverse along the sector. This process is achieved for the VPA in charge (diagram 5), We consider that the user has reached the VPA area, identify himself and requested the local route plan. Also the VPA reports the user credentials to the global PGB for registering and tracking purposes, The next step is to instantiate an generate a route plan based on the local OD pair requested by the user.

For this procedure the VPA is provided of local OD matrix database with updated time-varying parameters of arcs and nodes of the sector. The local route plan delivered to the users'

Sequence interaction for:

The Local Route-Plan

t U er

catcula� local_R�

VPA Service

Discovery

Response

(ID_User,ID_VPA, Route_Plan)

Report (ID_User,

ca Iculated _Route_PI a nJ

Response

(ID_User,ack)

�eve �e Plan

Report

(10_User, 10_Flow)

Register �user)

Request

(ID_sensor,

traffic data)

Response (ID_sensor, traffic_data)

Fig. 5. Local Route-Plan process

GPS will compute a predetermined route. This feature of dis­tributed computing assures scalability and avoid overwhelming the VPAs. Finally this process end with the collection of traffic data gathered from the traffic sensors. The gather of traffic data is performed periodically in order to maintain a consistent and updated database.

The local route plan consists in a sector-weighted map of arcs and nodes to be computed in the users' GPS with the known Dijkstra algorithm. The resulting path is reported back to the VPA and the instantiated internal flow path is also reported to the global PGB in order to maintain the tracking of flows where users are involved.

In general terms every VPA maintains an active OD matrix of origin (entries) and destinations (exits) defined for the arcs at the boundary of the sector (figure 6). In this sense every local route plan delivered to every user is dissimilar and is biased in such a way that enforces flow equilibrium. We consider that every sector has a weighted map with arc values by default. The user GPS share this common database, therefore the VPA only will transmit the affected arcs selected for each user. That is, a minimum list of specific weighted arcs is sent to every users in order to calculate a predetermined route inside the map sector.

Once the VPA assigns a route plans it will be aggregated into the active flows where enough capacity and faster travel time (minimum-cost) are available. The network flow is also updated from the feedback sent by user defined as:

• The user report their initial route plan, once it is calcu­lated by the onboard GPS.

• The network flow population is updated when the user reach their final destination or when its activity is no more detected.

• Every user reports its travel trip details at every VPA encountered on his way.

E . ,

1 ___________ _ ArC_ID, Weight

A, 2

B, 10

C, 7

� D, 5

E, 4 Sector bounda ry

-

Fig. 6. Local Route-Plan definition

IV. CONCLUSION AN FUTURE W ORK

Actual traffic networks evolve constantly in complexity and frequently with noxious emergent traffic behaviours. We focus in traffic guidance system as an instrument to enforce traffic management. Influencing and inducing drivers into auto­organized traffic patterns with common objectives: to obtain the best common travel time effort.

Actual ITS system provides solutions with proven technol­ogy. However this is costly, heavily to deploy and implement, and do not comply with global organization features for enhanced traffic performance.

Our solution is based on the handy role of police agents. These are empowered entities with specific purpose to provide local traffic control and global equilibrium, and governed by a global entity in charge to orchestrate maximum-flow with minimum-cost system conditions. This architecture is mainly devised to be used in environments with budget restraints such as rural ambient and cities in developing countries. The follow work consists to evaluate extensively the different use case scenarios partially implemented.

ACKNOW LEDGMENT

Research was sponsored by the National Council of Science and Technology, Mx (CONACYT).

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