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  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Designing a Serious Game of crisis management on top of an Agent-Based Simulation of population evacuation</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Mathieu Bourgais</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Arnaud Saval</string-name>
          <xref ref-type="aff" rid="aff2">2</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Pierrick Tranouez</string-name>
          <xref ref-type="aff" rid="aff2">2</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Olivier Gillet</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Éric Daudé</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>CNRS, Normandie Université, UMR 6266 IDEES</institution>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>INSA Rouen Normandie, Normandie Université</institution>
          ,
          <addr-line>LITIS UR 4108, F-76000 Rouen</addr-line>
          ,
          <country country="FR">France</country>
        </aff>
        <aff id="aff2">
          <label>2</label>
          <institution>University of Rouen Normandy, Normandie Université</institution>
          ,
          <addr-line>LITIS UR 4108, F-76000 Rouen</addr-line>
          ,
          <country country="FR">France</country>
        </aff>
      </contrib-group>
      <abstract>
        <p>Serious games have gained significant popularity, manifesting as board games or role-playing experiences designed to train individuals to think and respond in complex scenarios that are dificult to replicate and control in real life. Concurrently, numerous agent-based simulations are being developed to explore the potential dynamics of intricate systems through the behaviors of simulated actors. This paper introduces an innovative approach that combines these two methodologies; a serious game built upon an agent-based simulation focused on large-scale population evacuations, immersing users in realistic crisis management scenarios. This integration poses several challenges, as serious games require features that may conflict with existing simulation frameworks. These features include real-time interaction with the simulation, precise replay of scenarios, engaging displays to captivate players, and the capability to manage multiple users playing diferent roles simultaneously within the same simulation. To address these challenges, we introduce the ESCAPE-SG serious game. ESCAPE-SG is based on ESCAPE, a well-established agent-based model designed to simulate mass evacuations of populations from urban areas threatened by significant natural or technological hazards. We outline the challenges encountered and the solutions developed, particularly concerning the trafic simulation central to ESCAPE. Additionally, we propose a software architecture that facilitates the connection between the agent-based simulation and a front-end display, serving as an interface for users. This architecture ensures an engaging and interactive experience for players, enhancing the training and understanding of crisis management in transportation and trafic scenarios.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;Agent-based simulation</kwd>
        <kwd>Trafic simulation</kwd>
        <kwd>Serious Games</kwd>
        <kwd>Evacuation</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        Institutional actors may have to deal with major threats on their territory, whether of natural origin
(floods, tsunamis, volcanic eruption) or technological (toxic cloud emitted by industrial plant). Decision
making during these events is crucial to protect exposed people inside these areas. One way to get ready
for these extreme events is to train in advance, what is currently carried out through life-size training
courses for the whole crisis management unit [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ]. These training sessions often take the appearance of
serious games [2] where a scenario is played steps by steps with a careful analysis of results compared
to other solutions at each step.
      </p>
      <p>The primary goal of serious games, contrary to classical games where the objective is to entertain
users, is to teach new knowledge to players through their participation and interaction with the game
environment [3]. This means that even if a serious game looks like a classical game, for example using
pen and paper, a set of card or other kinds of pawns, the way it works answers other standards. Most of
the serious games take the form of a social simulation or a role-playing game [4] ; the game is run by
a game master who helps the players make decisions in a believable but stylized environment, then
the consequences of these decisions, which may put the game in a new state, are presented by the
game master. At the end of the game, the game master shows and comments the results so that players
understand what happened during the scenario they discovered. To increase the reality of the game and
the panel of available scenarios, the simulation of the environment may be done through a computer
simulation. The main issue is that none of the decisions made by players should lead to situations
not controlled by the game master or designers; each action must make sense in terms of the training
and coaching objectives, and the results of these actions, whether good or bad in terms of the game’s
objectives, must be, if not known, at least within the range of solutions accepted by the game designers.
The use of agent-based simulation models should help avoid this pitfall.</p>
      <p>Indeed, agent-based simulations are a meaningful framework for the study of a large variety of
situations where humans interact in a very detailed environment [5]. Just concerning the use case of
massive evacuation of population, there exists simulations of building evacuation [6], of cities evacuation
[7] up to evacuations of regions [8], with various level of decision making complexity for the agents [9].
All these simulations, with their many parameters and random processes, produce a vast amount of
data that researchers analyze to establish evolutionary scenarios based on probabilities of occurrence.</p>
      <p>ESCAPE is such an agent-based evacuation-oriented simulation framework [7]. It is aimed at
researchers whose works focus on the analysis of territorial vulnerabilities and mass population evacuation
strategies. It provides intuitive tools for building spatial and social data, as well as libraries in the GAMA
modeling platform [10] for fine-tuned modeling of mobility behaviors whether on foot, in a private
vehicle (car, motorcycle, bicycle) or in a public vehicle (bus). Coupled with the OpenMole software
[11], the ESCAPE suite can be used to explore numerous research hypotheses in "what-if" scenario
and "how-to" mode, such as a the evacuation from a volcanic eruption with the impact of ashes on
the road network [12]. ESCAPE requires the calibration of numerous parameters and exploration of a
large number of scenarios to produce territorial diagnosis and implementation of crisis management
plan. In this sense, ESCAPE is less a training tool than a support tool to evaluate diferent strategies
and policies, which is a challenge while switching it to a serious-game in respect to the mentioned
constraints. ESCAPE-SG [13] is therefore a serious game built on top of ESCAPE, but conceived and
designed as a training tool for crisis management over urban areas. To do so, multiple players have
to be able to interact with the running simulation of a city and its road network, with various roles
and diferent actions to perform. At the same time, a game manager should be able to run a scenario
adding external events dynamically during the simulated evacuation. Finally, the game should be able
to display the useful information in real time as well as ending statistics to measure the performance of
the decisions made and the actions taken. These conditions are not met with the existing frameworks
where detailed agent-based simulation of evacuation are implemented.</p>
      <p>Beyond the serious game itself, this article aims to describe the challenges encountered when
integrating a real-time interactive display, an agent-based model, and a trafic simulation, as well as the
solutions developed to address these challenges.</p>
      <p>Section 2 of this article discusses the previous works done with agent based simulations and serious
games, in particular in the context of mass evacuation in an urban context. Section 3 presents the
challenges which come with building a serious game on top of an existing agent based simulation of
an evacuation by describing how ESCAPE-SG has been built upon the ESCAPE and SUMO simulators.
Section 4 details the more general discussion about the implementation of such interactive device on
top of an existing agent-based trafic simulation. Finally, section 5 concludes the article.</p>
    </sec>
    <sec id="sec-2">
      <title>2. Related Works</title>
      <p>Agent based simulations have been widely used to study complex systems involving human decisions
and behaviors. They enable to recreate complex social and environmental situations and test various
conditions of evolution of such complex systems. This section focuses on the reviews of agent based
simulations and serious games about disaster risk management and population evacuation.</p>
      <sec id="sec-2-1">
        <title>2.1. Simulating population evacuation</title>
        <p>Evacuation of population under hazardous conditions is a case of social simulations [5] with an
importance given to the spatial dimension [14]: an evacuation starts with a situation under normal conditions
when something happens (it may be an alert sign or an sudden event) and people switch their normal
behavior to abnormal conditions. And these changes can be rapid and massive in the case of evacuation
in the face of ongoing or imminent danger (tsunami), or slow and gradual in the case of preventive
evacuation (slow flooding). Many works simulate the evacuation from the inside of a building with
hundreds of agents [9] [6]. Indeed a close environment with a fewer number of agents enables to
implement a more complex behavior, with cognitive, emotional and social dimensions as well as a fine
description of architecture and geometries.</p>
        <p>There are also city-scale simulations of evacuation. Taillandier et al. [10] simulate the evacuation
of an urban area under flood. Each agent represents a pedestrian trying to find a shelter from a flood,
following advises communicated by institutions. The same type of work may be done on a bigger
geographical area with a bushfire as the hazard to evacuate from [ 8]. Finally, Daudé et al. [7] propose
ESCAPE, a tool to model and simulate massive population evacuations in territories which can be
described by very descriptive land-use data, social data and network transportation systems. In ESCAPE,
agents which represent individual human may use diferent travel modes, starting as a pedestrian and
then driving a car for example, to achieve their goals. They can also travel by bike, motorcycle or public
transport, such as buses or subways. ESCAPE ofers a powerful Driving-skill pursuit model [ 15] and
the agents have evolving knowledge of their travel environment. They can thus have knowledge of
“experienced” trafic conditions, for example by memorizing the time spent by each person in trafic jams,
as well as more macroscopic trafic conditions, which allows some agents to benefit from optimized
routes such as can be provided by route optimization applications. This framework has been used to
simulate massive evacuation in the case of a volcanic eruption [12] and a flood [16].</p>
      </sec>
      <sec id="sec-2-2">
        <title>2.2. Serious Games and hazardous situations</title>
        <p>Serious games are playful activities which have, by learning, a serious goal on top of entertaining [3].
Learning is based on interactions with the model that simulates the crisis domain and on interactions
between participants to collaborate and succeed in solving a certain number of tasks. Marne [17]
proposes five common denominators for this type of game. The challenges are the problems given to the
player (for example, to protect the population from imminent danger); Significant actions correspond to
the steps taken by the player to resolve these challenges (for example, alerting the population, issuing
instructions or setting up evacuation routes); the game engine is the simulator which reacts to the
player’s actions; the graphical interface links the engine and the player which makes it possible to give a
playful aspect to both the problems and the simulator; finally, a script that allows the levels of dificulty
ofered to evolve according to the desired educational progression.</p>
        <p>Serious games have been applied in the field of risk management in order to rise awareness about
the consequences of catastrophes. In 2018, 45 serious games about disaster risk management were
surveyed [4]. This includes a board game aiming at raising awareness about environmental disaster in
the multicultural context of the Caribbean [18] or the "Don’t Stop !" video game where users play the
role of stakeholders who need to prevent damages before critical situation [19]. This latter video game
has been expanded lately on the more specific topic of evacuations in front of a flood [ 20], proving the
subject is still active in the community.</p>
        <p>Some serious video games (that is to say serious games that uses video games technique as their core
mechanics) rely on agent based simulations and multi-agent systems. Adam et al. propose a serious
game about urban planning in the context of sustainable transport in cities [21]. In this game, users
play the role of a group of people responsible for decisions on the urban landscape and the reaction of
the population living in the city is generated through a multi-agent system. This technical design may
be found in other works but specifically in the context of risk management and emergency evacuation
as with the SPRITE game[22] or LitoSim [23]. The goal is to take actions that will have impact on the
future catastrophe, the simulation is not in real time as the game simulate multiple months. With the
same principle in mind, Moatty et al. developed a serious game about the evacuation of a population
during a flood using an existing complex model of evacuation created with a multi agent system [10].</p>
      </sec>
      <sec id="sec-2-3">
        <title>2.3. Synthesis</title>
        <p>This section reviewed multiple agent-based simulations of large urban areas and evacuation of their
population, and then discussed some existing serious games about disaster risk management. However,
only few works combine these two field. From the simulation point of view, integrating game
mechanisms would help popularize their results to a broader audience. From the serious game point of view,
integrating an agent based simulation would make the result closer to a video game which is now a
powerful language to communicate complex ideas to people [24].</p>
        <p>One of the problem about using an agent based simulation into a serious "video" game in order to
study the evacuation of populations on large urban area comes from the technologies used. Even if
there exist multiple platforms to perform this type of simulation [25] [26] [27] [28], each with its own
strengths and weaknesses, these tools are not suitable to integrate a complex interface which enables
users to input discrete event into the simulation which operates in a continuous time. For example, for
game purposes, users may need to change the road network of a city during the crisis to deflect the
lfow of vehicles and open a path for emergency services. But doing so may create other impacts on the
overall road network of the city, which users should be able to react to.</p>
      </sec>
    </sec>
    <sec id="sec-3">
      <title>3. From Trafic Simulations to Serious Games: Challenges</title>
      <p>This section discusses the process used to create a serious game [15] about risk management by taking
its foundations in an existing evacuation simulation tool [13]. More specifically, the objective is to create
a multiplayer game where each player has a specific role and may take actions while the simulation of
a city, and its trafic, is running and reacting to the decision made.</p>
      <sec id="sec-3-1">
        <title>3.1. Simulating evacuation at a city level</title>
        <p>The ESCAPE project [7] allows to simulate the evacuation of wide territories exposed to a potentially
catastrophic events with citizens and civil servants (policemen, firefighters) represented by agents in
the system. It’s possible to first simulate the dynamics of the territory, such as the flow of vehicles
under normal conditions, before injecting an event (e.g. an evacuation order or a volcanic eruption)
that is perceived by agents, who will then react by modifying their behavior [29]. More precisely, the
ESCAPE project is composed of the following elements :
• Environment : the land-use (buildings, forest, river) and road networks of the studied area are
modeled. The pedestrian area are included as well as the type of the buildings (school, hospital,
residential, etc.) and the bus stops. A tool using R-Shiny has been developed to directly produce
environment data gathered from OpenStreetMap [30]. All these data are pre-processed before
being included in the model. Building the environment with open data enables to easily adapt
the project to a new use case.
• People : each human is represented in the simulation by an agent, and households are represented
as a set of agents. In order to create an agent population at a size coherent with demographic
statistics, a sample of real people is reproduced from census data. Generative synthetic population
libraries [31] are then applied to this sample in order to generate a population of the correct size,
with agents having characteristics as close as possible to the real studied population. This include
classical demographic information (age, gender, address) but also occupations over a whole day,
either for a working or for a non working day. The flow dynamics on ordinary days (i.e. without
any crisis situation) is reproduced using both household travel survey and trafic data measured
on the network. The agents’ occupations are described with a starting time, a mean of transport
and a location to reach at a specific time. For example, someone may take their children to the
school at 8 a.m. by car, go to their work place at 9 a.m. by bike, then buy some food at the grocery
store at 4 p.m. by bus, get their children from school at 5 p.m. by car and go back to their home
as soon as possible.
• Vehicles : each simulated person may use vehicles to move in the simulation, i.e. cars, trucks,
buses, bicycles and motorcycles. Each vehicle is modeled by a reactive agent whose mechanism is
to move from one point to another until it reaches its final destination, subject to compliance with
trafic regulations. Personal vehicles (cars, trucks, bikes, motorcycles) are created when a " people"
agent needs it and is destroyed once the travel has been done. Busses follow a timetable and they
go from one bus stop to the next one on their route, looping indefinitely. Each vehicle reacts to
its surrounding road conditions which means they stop if there is another stopped vehicle up
front for example.
• Hazard : hazards and theirs dynamics can be modeled directly or have their geographical footprint
uploaded from geographical information system as time-step layers defining their spatial and
temporal dynamics. Interactions between agents and hazards dynamics can be modeled to
reproduce casualties, or any impact on the environment (e.g. speed reduction) depending on the
catastrophe implemented.</p>
        <p>With ESCAPE, it is possible to simulate territorial dynamics, both in:
• Situation of ordinary mobility : each agent follows its own schedule for the day. This includes
going to work, taking care of their children who go to school, going to grocery store or going back
to their home among other activities. To perform these activities, agents may choose between
diferent mobility modalities depending on their starting and ending point. Once in a vehicle,
the shortest path to the destination is followed. Agents may use diferent types of vehicles to
go to their destination target (starting as pedestrian, taking a car, then a bus and maybe ending
with a bicycle). The vehicle is chosen based on the household travel survey as well as depending
on the lowest estimated time to move from one point to another. For example, the household
travel survey indicates that an agent takes a specific bus to go to a given location. Unfortunately,
because there is currently a trafic jam in the city, the bus is very late on its usual timetable. In
this case, the agent will evaluate if it is faster to wait for the bus or to choose another vehicle,
depending on the vehicles at her disposal.
• Situation of extraordinary mobility : when perceiving a hazard (either by seeing it, by hearing
an alarm or a message on the radio), agents may change their behavior and give up their normal
schedule. Depending on their own characteristics and the received message, they may either
choose between evacuating or confining. To do so, each agent may use multiple transportation
mode depending on the configuration estimated as the fastest to get to a safe place. Once a
decision is made, the agent integrates a vehicle that goes to the selected destination (either out of
the city or to the nearest shelter) by following the shortest path toward this target. When arriving
at a safe place, the agent is removed from the simulation.</p>
        <p>Operationalization of crisis management is modeled through various actions taken by authorities
such as the trigger of diferent types of alarms (global such as cell broadcast and local such as fixed
sirens or mobile alarms). These alarms may be heard by people at a given distance who in return will
decide to follow or not instructions. This means that not all agents either evacuate or confine shortly
after the notification, but may still pursue their activities. This decision making process is fixed by the
modeler through the use of diferent parameters or probabilities functions provided by ESCAPE tools
and calibrated upon population surveys [12].</p>
      </sec>
      <sec id="sec-3-2">
        <title>3.2. From ESCAPE to ESCAPE-SG</title>
        <p>The ESCAPE project has been expanded into the ESCAPE-SG serious game [13] [15]. The main goal of
this operation is to create a training tool which is more understandable than a simulation, but provides
realistic dynamics and scenarios. The key features of the ESCAPE-SG serious game are:
• The overall setting is the evacuation of an urban environment, from a part of a town to a few
nearby towns. For this, players should be able to interact with the running simulation (e.g. to
close a road, to check information such as the number of peoples in a shelter or to select antennas
to switch-on the alarm system).
• Several players, each with a dedicated role (i.e. mayor, civil servant, road manager), should be
able to play together on the same simulation at the same time. They may act on a medium or
large scale: evacuate such or such building or area, block a road, intervene on a fire, etc. but the
evacuating individuals are ran by the simulation. Likewise, a game manager should be able to
trigger events during the game (adding a car crash, worsening or improving the hazard condition,
creating a new hazard).
• The trafic situation inside the simulation should be displayed according to diferent time frames:
one in which simulated time is equivalent to real time to clearly understand the impact of a
player’s decision, and also discrete (x3, x10) or continuous (from 1 to 10) accelerated modes
that allows to stay within game duration consistent with the time allowed by players or game
managers.
• Taking the fact that each role has its own actions available, players need to have feedback from
the game to understand the consequences of their actions.</p>
        <p>Although the primary version of ESCAPE includes its own multimodal trafic and transportation
model, ESCAPE-SG utilizes the ESCAPE model by incorporating the SUMO platform [28] for trafic
simulation. Additionally, it employs a custom multi-agent system in JAVA to manage detailed individual
interactions between mobile agents, extending beyond the capabilities of SUMO. This MAS acts as an
intermediate between SUMO and the Unity game engine [32] which is used for the ESCAPE-SG 3D
graphics front-end. Indeed, the ESCAPE simulation is running on the GAMA platform which does not
enables to easily act in multiplayer upon a simulation running in continuous time. If GAMA graphical
interface allows to display simulation information, it is not meant to manage intensive graphical inputs
from several players at once. It is also not able of synthesizing inputs from several disjoint graphical
interfaces computed on distant networked computers. Finally, GAMA cannot be either interrupted or
resumed, nor have its internal values modified by external programs. It was as a consequence not the
right software tool for the back-end of ESCAPE-SG.</p>
        <p>Figure 1 shows the screen of the game manager watching a particular spot on the road network
within ESCAPE-SG. Buildings and vehicles are displayed in three dimensions and the interface shows
the various actions which may be taken. Each user watches a similar screen but may focus on an
other place of the same simulated area. They may access only their available actions. Figure 2 shows a
more macroscopic view of the simulated territory, in which trafic conditions may be distinguished,
synthesized here by color gradients on the sections (red indicates trafic jam, yellow means congested
trafic, green symbolizes a fluid trafic flow). At this scale, diferent players can perform actions on
diferent parts of the territory at the same time: closing a motorway, triggering a siren in the city center
or ordering a noria of buses to evacuate a retirement house.</p>
      </sec>
    </sec>
    <sec id="sec-4">
      <title>4. Generalizing the process</title>
      <p>Section 3 presented a use case where a serious game is built upon an existing agent-based simulation of
a city evacuation. From this use case, this section discusses in a broader way the challenges related to
the development of a serious game starting from an existing agent-based simulation of an evacuation
situation of a city. The goal of this section is to present a general software architecture to ease the
development of future interactive simulations, such as serious games, especially in the domain of
mobility, as well as exposing the underlying challenges that arise.</p>
      <sec id="sec-4-1">
        <title>4.1. Simulation versus serious game</title>
        <p>Agent-based simulations and serious games focusing on the same phenomenon do not have the same
objectives, and so they do not use the same tools. Studying a situation with the use of simulations has
the following goals :
• Realism: a simulation must recreate as closely as possible the behaviors of the studied situation.</p>
        <p>Fostering realism may lead to the development of complex decision making models for the
simulated agents which may be dificult to explain from the point of view of an observer.
• Validation by data: beside demonstrating realistic behavior for the agents simulated, a simulation
needs to be validated against data for a specific scenario on a real use case. This implies accessing
these data beforehand and sticking as close as possible to this case. This statistical validation,
coordinated with the realism of behaviors, implies once again to sacrifice a bit of explainability
from the system if necessary.
• Exploration of non monitored circumstances: once validated on its behavior and its
calibration, a simulation enables to explore unknown situations, either because they are currently not
monitored in real life or because they rarely happen. The goal is then to make predictions on
"what if" scenarios which would serve to validate the behavior of the model.</p>
        <p>On the other hand, the main objectives of a serious game about a similar situation are :
• Education: the primary objective of a serious game is to teach something to its participants.</p>
        <p>This may be about the consequences of a particular situations and how to handle them or about
what to do to face a given situation. To do so, a scripted scenario, which may be an exaggeration
of a real case, is at use.
• Gameplay: a serious game is still a game. Its gameplay, that is to say the rules enabling players
to interact with the state of the game, is crucial to create an enjoyable experience. This may
implies to alter the realism of the represented situation for pace consideration and simplicity of
actions.
• Exploring scenarios: to ensure the game may be played multiple times by the same players, for
teaching reasons, multiple variations of the same situation should be scripted. Each game may
explore a new variation of the same overall scenario. These scenarios are created for the notions
they may teach, not for their validity with existing data.</p>
        <p>Because their objectives difer —simulations aim to mirror real data as closely as possible, while
serious games seek to create engaging educational experiences— their technical constraints are not the
same. Taking the study of urban trafic as an example, an agent-based simulation will attempt to include
all human actors as agents and compute a complex decision-making process that closely resembles
human decision-making, even if it takes several days to simulate a few hours of trafic. The results are
obtained after all computations are completed and are then compared to real-life data.</p>
        <p>In contrast, a serious video game addressing the same urban trafic scenario needs to condense several
hours of the studied situation into a few minutes to remain enjoyable. To achieve this, the studied
area may be smaller, with fewer agents and simpler behaviors, allowing computations to be performed
nearly in real time. The game’s response to players’ actions, which is crucial for the serious game,
should also be displayed in real time so players can adapt their decisions accordingly.</p>
        <p>Szczepanska et al. [33] define six ways to create a collaboration between an agent-based simulation
and a serious game; the ESCAPE-SG project and the challenges discussed in the current article fit in the
third design type with an existing simulation at the origin of the game.</p>
      </sec>
      <sec id="sec-4-2">
        <title>4.2. Creating a serious game from a simulation</title>
        <p>As mentioned previously, one of the main challenges to create a serious game from an existing trafic
simulation deals with the fact that players have to perform their actions while the simulation is running;
in other words, this means triggering discrete events over a continuous simulation. The problem is then
to have a computation time close to real time while keeping as much as possible the complex behavior
of the simulation.</p>
        <p>Figure 3 shows the software architecture developed to ensure that players could act over a running
agent-based simulation from an interactive interface. The system may be decomposed in three parts :
the back-end where the simulation runs, the front-end which serves as an interface with players and an
API which makes the connection between the back-end and the front-end. This figures displays at the
same time the overall general architecture as well as the specific technological choices made for the
ESCAPE-SG project which are discussed in section 3.</p>
        <p>To ensure at the same time low computation time and a complex decision making process for each
agent, the back-end side of the architecture is decomposed in two parts, as seen on Figure 3. The basic
trafic simulation is managed by a dedicated trafic simulator. At this level, vehicle agents have a simple
reflexive behavior in which they have a target point to drive to using the shortest path computed on
advance on the road ordinary network (no road is closed). They follow road trafic regulations with a
reactive behavior and do not make complex decisions. Agents not in movement are not included.</p>
        <p>The complex decision-making process is managed by a dedicated Multi-Agent System (MAS). This
MAS computes the actions of each agent at every time step. Primarily, each agent follows its own
timetable, which is not very demanding in terms of computation time. When an agent starts a new
activity, the MAS determines how to carry out this activity, including which mode of transportation
to use, taking current conditions into account. Once a decision is made, it is communicated to the
simulator, which may then move the agent within a vehicle on the road network. In a crisis situation,
the agents will react according to the ESCAPE model [7], based on the various possible alert systems,
by communicating with their social network and planning evacuation or confinement.</p>
        <p>The MAS then transmits the positions of moved agents to the API, which serves as a connection
point with the front-end part of the architecture. This API may also host multiple services accessible to
all front-end users, such as a chat system that enables players to communicate with each other if they
are in diferent locations.</p>
        <p>On the front-end side, each user has its own client displaying a graphical interface. Depending on
the role of each player, the actions available upon the simulation are diferent. Each action performed
at any time by any player is sent to a REST API as a command. This command is then passed on to the
MAS which modifies the environment settings. The set of commands includes closing a road, changing
the direction of trafic, opening shelters or triggering alarms for example.</p>
        <p>Lastly, the game manager has a dedicated interface. With a dedicated set of actions, the game manager
may run a given scenario acting on the environment or the hazardous condition by sending commands
to the API. This way, the game manager is seen as a player with a specific role.</p>
      </sec>
      <sec id="sec-4-3">
        <title>4.3. General discussion</title>
        <p>To ensure an eficient serious game, in regard to the notions learnt by participants, it is important to put
the player as close as possible to the real case situation [4] while having a multiplayer experience [34].
These two principles guided the creation of the modular software architecture described by figure 3.</p>
        <p>Beside ofering a complex agent’s behavior with a low computation time, this modular approach
enables to make dynamic modifications to the simulated environment in live conditions. A player may
want to close a specific road to redirect the trafic flow during the simulation. The action is selected
on the graphical interface which sends the command to close a given road to the MAS, through the
API. The MAS translates this action by removing the road from the network. However, this action may
change the shortest path of some vehicles. The MAS takes in charge to recompute the shortest path for
the concerned agents (i.e. agents which actual path include the closed road). On the simulator’s side,
nothing changes as it receives the new target communicated by the MAS.</p>
        <p>To ease the process from the point of view of players, and increase the realism of the game, these
actions are difered between their decision and their efective realisation. Let’s take the same example
of action: closing a road with the mayor’s role while the evacuation has started. In real life, closing a
road implies giving an order to a worker who needs to travel to the selected point and then places a
sign indicating the road is closed, a whole process that could take multiple minutes. To mimic the real
world, the player needs to implement this action by selecting the specific road to close which efectively
closes a few minutes after the order was given. Multiple actions follow the same principle: either their
efect is difered in time or their consequences will start to have an impact multiple minutes after they
were decided. This type of difered action ofers time for the MAS to compute all the modifications to
the agents behavior, and applying it seamlessly once the action is efectively executed.</p>
        <p>The same problems arise on the game manager side: the hazard triggered have an efect over
the simulation for multiple hours. Hence, the simulation flow of time should be altered in order to
have a game covering multiple days around the catastrophe playable in few minutes/hours. With an
architecture making a diference between the atomic computation of the next move and the decision
making process, it is easier to pause the simulation or fast-forward it; as each part is waiting for the
other, a command may be passed to one part which may disconnect until it is executed.</p>
        <p>To sum up, connecting a graphical front-end to an agent-based simulation implies the use of a
dedicated MAS created depending on the features wanted. Each interaction ofered to users would
need to redefine a part of this custom MAS. While the MAS is deciding what each agent needs to do,
the simulator may continue to make agents do basic movement, and so users are not disturbed by a
simulation pausing itself to compute the next step.</p>
        <p>Finally, the goal for realism of the game also implies a complex graphical user interface. In real life,
stakeholders have a partial knowledge of the events. By implementing one client per role, each player
has access to only partial information from the simulation and needs to communicate with the other
players before making a decision. With the same principle, each role only has access to a sample set of
all the possible actions, reflecting its real life capacities. All these reasons imply the use of a front-end
which is not integrated with the back-end, a modularity that eases a personalized display.</p>
      </sec>
    </sec>
    <sec id="sec-5">
      <title>5. Conclusion</title>
      <p>This article describes the creation of the serious game ESCAPE-SG [15] from the ESCAPE project [7] as
an initial use case. This particular case is used to extract a more general discussion on the challenges
arising when building a serious game from an existing agent based simulation, especially in the field of
trafic simulation. Specifically, the main objectives of a mass evacuation simulation are not the same
as a serious game, which implies the proposition of a dedicated software architecture to create a link
between these two fields. Dealing with a trafic simulation at the center of the serious game adds
problems related to the dynamic of the system that needs to quickly adapt to actions taken by players.
The software architecture proposed in this article helps to deal with these issues by implementing a
custom Multi-Agent Systems which manages the decision-making process of each agent, creating a link
between a dedicated and simple trafic simulation, and the graphical interfaces of players.</p>
      <p>A scenario over a technological hazard in the city of Rouen in France is already implemented with 10%
of the real population simulated. However, this scenario has not yet been tested with crisis managers
to assess its capacity to improve the existing training sessions. In the future, new scenarios on new
areas will be implemented in ESCAPE-SG to demonstrate the generic nature of the project. Also, a
more precise study will be conducted on the integration of trucks in the simulation and a rewind action,
which would enable to come back to a previous state of the simulation, will be tested, creating new
features to integrate to the dedicated and custom MAS.</p>
    </sec>
    <sec id="sec-6">
      <title>Acknowledgment</title>
      <p>This work is supported by the ANR ESCAPE project, grant ANR-16-CE39-0011-01 (French Agence
Nationale de la Recherche), by the RIN Tremplin ESCAPE-SG project (Région Normandie) and by Grand
Plan d’Investissement TIGA Mobilité Intelligente Pour Tous.
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