Cyber-Physical Urban Mobility Systems: Opportunities and Challenges in Developing Countries

Rapid population growth and the number of vehicles in cities have complicated urban mobility management. Digitalization supported by the internet of things and wireless communication has allowed some cities to mitigate the problem by taking advantage of the multiple benefits offered. These are cyber-physical systems (CPS), which are systems where a number of devices collaborate for the control of physical entities. This recent technology finds its application in urban mobility. However, in the context of developing countries, there are many local specificities one needs to consider. How could the integration of cyber-physical systems help urban decision makers to design sustainable urban mobility systems that meet the needs of the population? The paper proposed not only a recent review of the literature, but also a framework of CPS of urban mobility to guide decision makers. The challenges, opportunities, and barriers to innovation of CPS in urban environments in developing countries have also been identified.


INTRODUCTION
According to United Nations projections, by 2050 almost 70% of the population will live in cities (Cohen, 2006;Van & Marston, 2021). Moreover, these cities suffer from congestion, road accidents, high travel times, and air pollution (Monios & Bergqvist, 2020). These urban mobility problems are common in both developed and developing countries. But in developing countries, the situation is literature on cyber-physical system technologies and its application in the field of urban mobility, but also aimed to propose an architectural framework of cyber-physical urban mobility system in the context of developing countries to respond into integration systems challenge in the domain of transportation. Finally, the paper highlights some of the challenges and open research problems in the field of cyber-physical urban mobility systems in the perspective of designing an intelligent and sustainable mobility system that best meets the needs of users.
The rest of this paper is organized as follows. In section 2, the background of CPS technologies is presented, followed by its application in the field of urban mobility and related work on the design of urban mobility systems in section 3. Section 4 presents the methodology used to select articles from different databases. Section 5 presents the design of the architectural framework of the urban mobility system in developing countries and finally section 6 presents the challenges and opportunities identified for the design of the system as well as the perspectives. Finally, the conclusion and research perspectives are presented.

CPS Technologies
CPS technologies aim at integrating computation, communication and control capabilities with an engineering system (Cheng et al., 2018;Zhu, 2022). For this reason, IoT devices are considered the basis of CPS technologies (Jeschke et al., 2017). It is important not to confuse IoTs with CPS technologies. IoTs put more emphasis on objects connected through, which for CPS emphasizes the integration of computing, communication, and control capabilities to (un)connected physical objects. But at the same, IoT enables interconnection of devices through the network to share data, computing, and control objects (Gupta & Godavarti, 2020).
The concept of CPS has appeared in the first time in the United States in 2006 with the aim of making the network of systems interact with the physical world (Lee, 2006). This new paradigm is differently defined by scholars in recent works. According to (Gupta et al., 2019), CPS are distributed systems in constant interaction with their physical environment through detection. For (Kantarci et al., 2015), a CPS paradigm is a product resulting from the fusion of physical process and computer programs at multi-scale multilevel. For these authors, CPS aimed to extend the controllability, efficiency and reliability of a physical process. Emerging CPS applications are numerous, and are driven by the expansion of information communication technologies (ICTs) tools, mobile internet, Open Data, Big Data, artificial intelligence (AI), Machine Learning (ML), Cloud Computing (Ramasamy et al., 2022). Among so many CPS applications, there is the urban transportation domain high interests us in this paper.

CPS Applications in Transportation System
In the near future, CPS technology will be used for integrated urban mobility (Moller & Vakilzadian, 2016). Therefore, solutions to urban mobility problems require CPS to improve performance of a transportation system. Today, the development of mobility as a service (MaaS) based CPS technology has enabled the convergence of different transportation means, ticketing systems, and a web-client application to users to satisfy them (Deka & Khan, 2018;Bellini et al., 2022). This technology is able to control road traffic to reduce road accidents, congestion, and air pollution. Human errors on the road are multiple (Khattak et al., 2019). So it is very difficult to meet the expectations of pedestrians and drivers in terms of road safety. CPS technology may help humans to manage road traffic with the support of sensors or drones and actuators (Ari et al., 2016;Nouacer et al., 2020). In addition, the CPS-based transport system can be used to solve the last-mile problem, whose access in landlocked areas does not allow vehicles, but rather motorcycles and bicycles. To master the variety of disturbances on the road in developing countries and the very high number of interactions in the 4 integrated transport system, a CPS-based urban mobility can improve the traditional mobility system with the integration of transportation infrastructure and connected objects with computer programs for their control. The main application areas of CPS in transportation system are presented below.

Cyber-Physical bike
According to the United Nations report, cases of bikes and motorcycles accidents are very fatal for drivers and passengers (Sirajudeen et al., 2022). The use of CPS technology coupled to the bike has made it possible to embedded video cameras and actuators to continuously monitor the cyclist's surroundings, and receive alerts in the event of danger (Smaldone et al., 2011). These alerts may improve road cycling safety and real-time detection of disturbances. Thus, a Cyber-Physical bike has video processing capabilities to perform automated rear-approaching vehicles detection. Other researchers have also proposed an intelligent control system to be integrated into smart bicycle in order to manage the interactions between the physiological behavior of the cyclist and the urban environment (Mannion et al., 2019). Mannion et al. relied on the pitchfork bifurcation system to design their on-board bike control system.

Vehicular Cyber-Physical
The problems of vehicle collisions and risk turns are numerous on the roads (Halim et al., 2022). Researchers have taken advantage of advances in real-time computing, software defined networking (SDN), blockchain, and machine learning to improve vehicles in driving experience with CPS-based models, which are able to manage interactions and disturbances through feedback-driven regulation (Bradley & Atkins, 2015). Other researchers have turned vehicles into mobile cloud computing, which allow interactive travel, pedestrian protection, and efficient driving (Jeong & Lee, 2014). However, vehicular cyber-physical systems (VCPS) applications include assisted driving, safety applications, self-driving, emergency communications, and infotainment (Rawat & Bajracharya, 2017). Thus for driving assistance for example, (Chen et al., 2020) proposed a fuzzy Markov model for road guidance to predict traffic problems.

Traffic control based Cyber-physical system
Control is a very important characteristic of CPS technology (Verma, 2022). Researchers have proposed CPS-oriented systems to traffic control. The studies carried out try to solve the major challenge based CPS when controlling traffic, the coupling of transportation behavior theory, information theory, and computer programs with computing, communications, and control capabilities (Jianjun et al., 2013). Jianjun et al. suggested that a proposal traffic control must manage three major components: traffic system control, traffic signal control, and traffic behavior control. (Farradyne, 2000) proposed traffic management application to manage the traffic flow for safety of motorists, pedestrians, crash victims on roads traffic. For Farradyne, coordination in Public transport is able to increase traffic efficiency and management of traffic flow, monitoring vehicles, and road conditions. In the same way, (Li et al., 2020) suggest that traffic management-based video cameras responds to traffic incidents prediction for example interference control in Inter-Vehicle Communications.
(Rebeiro et al., 2020) proposed spatial distributed IoT-based monitoring of urban air quality to protect the health issues resulting from urban environment pollution. Road monitoring systems refer to the systems in charge of supervising vehicles, road traffic conditions and air quality. Table 1 below summarizes some works based on CPS that have effectively contributed to improving urban transport. Table 1 presented some works related to the management of transport systems based on CPS. The authors are interested in specific aspects (intelligent vehicle, security measure on wireless technology, privacy preservation, recommender system) of the transport system to improve the quality of mobility. The following section presents the CPS architecture models used in different study areas.

CPS Architecture Models
The cybernization of complex engineering systems requires the design of reliable and efficient architectures (Parri et al., 2021;Hunke et al., 2021). Convergence system aims at the large-scale integration of physical objects with computer programs, it called cyber-physical systems (CPS). The specific paradigms CPS applied to various domains are shown in Table 2. In the recent works, CPS  (Yaacoub et al., 2020). The fourth industrial revolution aimed to improve human life and health where manufacturing, big data analytics together with augmented reality diagnoses patients with health irregularities and ascertain prognosis (Nayyar & Kumar, 2020). Industry 4.0 incorporates technologies like 3D printing, advanced robotics, cyber security, big data analytics, augmented reality, industrial internet of things, cloud computing, cyber-physical systems, horizontal & vertical integration to the production process of the industry (Kumar & Nayyar, 2020). All these technologies will allow industry 4.0 to offer ease understandable, increase reliability and efficiency, better accessibility, ease use, safe for everyone, customized products, and agility.
With the fourth industrial revolution, education must be transformed into Education digitalization to allow pupils or students to learn in various places and respective places, to personalize the training modules according to their abilities, to use tools for distance education, collaborating in the learning process with other learners, and more (Nafea & Toplu, 2021). So, the engineer from digital education will acquire interdisciplinary skills to easily address the problems of complex production systems. CPS technologies will bring quickness in the acquisition and competence of the learner for a very competitive know-how in enterprise. For example, (Mäkiö-Marusik et al., 2019) shown a novel learning and teaching concept "T-CHAT" that allows future engineer to acquire interdisciplinary knowledge and skills as well as a multidisciplinary view for being able to run industrial digitalization projects successfully.
Systems integration raises data protection concerns around the world (Wlazlo et al., 2021). IT protection covers the life cycle of data in the system. The democratization of the Internet has increased threats and attacks, for example the man-in-the-middle. Man-in-the-Middle Attack is a type of cyberattack in which an unauthorized person enters the online network between the two users, avoiding the sight of both users (Narula et al., 2022). Wlazlo et al. shown how man-in-the-middle attacks can cause misguided operation and false measurements in an emulation-based cyber-physical power system against a smart grid model. Wlazlo et al. presented method to detect man-in-the-middle attack traffic by correlating Snort intrusion detection systems alerts with address resolution protocol and distributed network protocol-3 packet data, using network metrics such as retransmission rate and average round trip time. Countries have used cyber security to protect their computer systems with the five basic principles of computer security: confidentiality, integrity, authentication, non-repudiation and availability of information.
To essentially improve human well-being, scholars have studied the social factor. For example, (Wu et al., 2014) studied an emergency system to improve human factor. Wu et al. proposed Cyberphysical human system architecture to predict and control human. The same authors have also proposed in medicine a Cyber-Physical Human Medical System architecture for zero safety-critical human problems in the medical system interactions. (Gong et al., 2022) proposed CPS based human to satisfy the well-being of a human. Authors called it Cyber-physical-social system. (Sanchez et al., 2017) proposed CPS to ubiquitous sensing and gathered physical information about the environment or human social activities, called Cyber-Physical Social Sensing. (Cardin et al., 2019) proposed a high-tech enterprise production architecture based on CPS technology. Authors proposed Cyber-Physical Production Systems to provide intelligence, connectivity and responsiveness for production enterprise.

STATe OF ART OF CPS IN URBAN MOBILITy SySTeM
In this work, a total of 1470 published papers were studied. Following techniques for filtering duplicates and papers poor in content, 77 papers were selected following the procedure described in Table 4.

Sustainable Urban Mobility Systems Design
Studies on the design of sustainable mobility systems have not interested scholars too much over the ten last years. And yet, the design of such a system is a very complex problem in transport engineering, civil engineering, and computer science. A sustainable mobility system stands for a mobility that contributes positively to the economy of the region, without compromising human health, environment, or the ability of future generations to meet their needs (Da et al., 2008;Yetim et al., 2020). Urban mobility must consider alternatives to private vehicle in order to reduce the pressure of motorized traffic on roads and the environment. However, (Ngossaha et al., 2020;Moskolaï et al., 2019) classified the approaches to the urban mobility systems design into two categories, (1) approach by sectoral analysis, and (2) global system-oriented approach. For authors, approach (1) does not bring visibility into the entire system, but rather creates conflict between the subsystems that can affect the efficiency of the mobility system. Approach (2) facilitates the control of the resilience of the system. Other studies have been conducted to propose new approaches to improve the urban mobility system. (Wegener et al., 1994) proposed an analysis of the dynamics on the change of state of the mobility system based on the non-formal specification of the system. This approach considered the complexity This paper Cyber-physical urban mobility Systems urban mobility system engineering design, architectural framework design, modeling and simulation, formal verification and validation, multi objective optimization of the system, even if it remains very limited, the management of interactions between several areas of mobility and the evaluation of the mobility coverage rate. (Goldman et al., 2006) used a global approach to analyze the socioeconomic impact of urban mobility which remains frozen in the management of complexity with socio-economic impact. It presented efficiency, management gains and efficient monitoring of mobility actions. (Jifeng et al., 2008) proposed an analysis of the dynamics of the mobility system based on the non-formal specification of the system. The limits of this approach are based on the management of the complexity only limited to the field studied. Interactions are not very representative of the whole system, and its representation is ill-suited to understanding it. (Ngossaha et al., 2020) proposed a holistic approach considering the entire lifecycle of sustainable urban mobility system. Ngossaha et al. have subdivided the system into four subsystems: (i) the topology of the urban mobility system; (ii) the timetables of the urban mobility system; (iii) the urban mobility services; and (iv) the management of the urban occupation of mobility. Ngossaha et al. have developed a meta-model for a sustainable mobility system and propose a method for deploying the distributed architecture of the system. The proposed solution is a decision support tool for the city in the implementation of the urban mobility system for the future. Authors integrated the management of the system complexity by considering the interdisciplinary expertise and multidisciplinary domain. Unfortunately, the authors did not prove the validity of their proposed system architecture by modeling and simulation.
Finally, the mobility paradigm has evolved over time ( Van et al., 2018). The twenty first century marks the fourth-generation mobility era. This new mobility relies on the sustainability, integration, intelligence, and autonomy of urban mobility system. For this reason, the urban mobility 4.0 design requires to reconcile the interests of the approaches proposed in the literature and to consider partially/fully the gaps cited in the proposed solutions: (1) the coupling of control, communication and data processing systems in the transportation system; (2) improving the analysis of the complex interactions between the different components of the system by taking into account the quality of the exchanged flows (energy, material, information and even geographical location) and the specific local requirements. This situation leads us to share the point of view of , who defines urban mobility system as a complex system of systems that encompass physical and non-physical components that can work together to enable dynamic, real-time complex interactions between urban subsystems such as transportation, energy, healthcare, housing, food, entertainment, work, social interactions, and governance. So, the sustainable urban mobility system design must take account variables as the spatial pattern of human settlements, activities at a particular point of time, socioeconomic and socio-cultural variables, non-connected (or connected) vehicles, bike-sharing system, mass transit, pedestrians, transportation infrastructures, transportation services providers, transactional environment and others (El-Sherif, 2021). This convergence and integration of systems reveals a new concept called Cyber-Physical System. The following figure (Fig. 1) shows an example of a CPS.

Main goal and Position
Considering the literature review, the implementation of an urban mobility system is a complex engineering task. However, important aspects should be considered when designing such a system, for example the economy, the socio-cultural context, local technological innovations, the environment, and more. Many approaches have been studied and presented in the Table 3.
Recent work has developed much more specific aspects of the transportation system. However, the urban mobility system is characterized by complex interactions between sub-systems. A holistic consideration of the system will allow to anticipate emerging phenomena in mobility systems that are sources of road insecurity and time loss. Thus, none of the approaches considered in the works studied considers the management of complex interactions and social collaborations in an urban environment. To this end, a methodology based on CPS coupled to the urban mobility system is needed in order to better consider the physical, informational and decision-making aspects in the  design of mobility systems. A synthesis of the literature on the design of urban mobility systems, the proposal of a new architectural framework and the identification of challenges and opportunities related to new technologies for mobility are the major objectives of this paper. These contributions will help mobility decision-makers in the design of systems that federate all physical components with computer programs to enable real-time control of mobility and consequently meet the needs of users in the context of developing countries.

MeTHODS
The study was developed based on scientific work published between 1969 and 2022. The compilation of a collection of keywords are used to form queries combining logical operators such as, OR and AND. For example, CPS OR ITS, Smart mobility OR ITS, and more. The queries formulated are entered into Google scholar search engine to download references papers from respective IEEExplorer, Springer, MDPI, ACM, and Web of Science databases. The results from the method are described in Table 4 bellow. Clearly, the method is based on six processes. The process one identifies the different possible keywords related to the subject to be treated. For example, CPS, Intelligent transportation system (ITS), Mobility as a Service (MaaS), and more. The process two performs information research based on the keywords selected via the search engine Google scholar. The process three consists in breaking down the documents gathered by journal IEEExplore, SpringerLink, ACM, ScienceDirect, MDPI and Web of Science. The process four consists in applying a reading filter to remove unnecessary files among the various downloaded documents. For a document to be retained, it had to develop aspects on the ITS, the opportunities and challenges on the scope of application of CPS to transport, transport in developing countries, the paradigm of sustainable urban mobility, and the architecture of CPS. The process five merges the selected documents. And in the last process, it is a question of simply eliminating the duplicates by the documents.

ARCHITeCTURAL FRAMewORK OF CyBeR-PHySICAL SySTeM IN URBAN MOBILITy: CASe OF DeVeLOPING COUNTRIeS
The context of developing countries is a huge challenge to take up, especially since all the aspects have to be redone (Mfenjou et al., 2018;Holzinger et al., 2021). An architectural framework for CPUMS is shown in Fig. 2. The architecture brings out three main important dimensions for efficient numerical convergence and control system: (1) decisional dimension responsible for coordinating between public and private partners, (2) infrastructural dimension to meet users' expectations, and (3) informational dimension responsible for providing a digital platform for MaaS. So proposed architecture is composed in details with coordination of CPS decisions, urbanization information systems, vulnerabilities of users and public administration, collaboration, coordination and interoperability, and process optimization. Coordination of CPS decisions makes it possible to coordinate the management of interactions between connected objects (vehicles, communication infrastructure, surveillance cameras, and traffic lights). Drivers need real-time information about the traffic situation to make decisions, and passengers desire transportation services to which the system should recommend solutions to satisfy passengers' needs. The stakes for this module are enormous for the robustness and reliability of the intelligent and flexible system.
Urbanization Information Systems is based on urbanization of cities and land use. It provides flexibility on the transportation system to ensure: 1) its evolution, 2) its modularity, and 3) its renovation, while preserving the functioning of the system. It enables communication control, costs reduction. Therefore, this module aims to creating an agile, flexible and scalable information system for proposed architecture CPUMS. The impact of the construction of additional roads and their tarring has proven to be less important, because road accidents are still current events. This module brings here the possibility to digitize the urban systems, for much more intelligent in the management of the mobility and the decision-making.
Vulnerabilities of users and public administration is responsible for integrity checking, consideration of socioeconomic requirements for human urban mobility. The most venerable social stratum is the poor, the elderly, and the handicapped. They suffer from the impacts of air pollution on the roads, and the high cost of transportation. The intelligence and hyper connectivity advocated by CPS technologies are able to problem solving.
Collaboration, Coordination and Interoperability simplify the process of evolving complex engineering subsystems, communication languages specification, interactions control and management between subsystems or components to ensure system interoperability.
In developing countries, the road is a social good. Priority and the rules of the road during crossings are neglected in favor of precipitation and bifurcations, major causes of mobility problems. Optimization processes can develop optimal transport theories for reducing travel time, promoting multimodality, carpooling, smart parking, traffic jams and errors for these countries. The system suggested in this paper is composed of subsystems that may have the ability to communicate, process data and control objects through computer programs. Fig. 3 shows an implementation of the proposed architecture.
The system proposed has three essential elements: the cyber world, the physical world and the multiform interconnection links (microwave links, optic fiber distribution networks, local area networks or 4G/5G/LTE network). The decision-making system includes the transport management center, emergency management services, weather and street condition services, multimodal management services, the data processing center and urban big data. The physical world includes transport infrastructure, pedestrians, vehicles, bicycles, animals and ICT tools (drones, sensors, RSUs, routers). Figure 2 and figure 3 can be mapped by the physical representation below (Fig. 4) to show how the interfaces are implemented among the constituent components.

. Complex interactions between interfaces of components in CPUMS
Transport Management Center (TMC) is responsible for monitoring road network conditions and traffic control. TMC exchange with the global system with secured transportation network. Emergency Management Services (EMS) represents systems that launch alert or incident order to the transport management center. EMS manages sensors, drones, RSU and video cameras to enhance safety transportation. Weather services and road conditions presents road conditions and meteorology. Computing unit is responsible for real-time computing operations in the system. Multimodal Services integrates intelligent vehicle parking services and the carpooling management system. Processes optimization event is responsible for providing demand responses for shortest path, intelligent traffic light optimization, optimized driving assistance.

CHALLeNGeS AND OPeN ReSeARCH ISSUeS OF CPUMS
Urban mobility system design is one of the complex tasks for government or engineer transportation. Urban mobility has undergone many changes, ranging from era of horse-drawn carriages to the era of digital mobility. CPS is the bedrock of the fourth-generation industry today. The CPS coupled the physical infrastructures of the transport to the computer algorithms for their efficient and effective controls. However, the use of solutions based on CPS pose enormous challenges, especially in the context of developing countries. These challenges relate to the deployment and optimal connectivity of connected objects, location mobile objects, management of quality of services, development of optimization processes for optimal transport, collaboration between connected (non-connected) objects, interactions and disturbances management, computing, implementation and validation of the architecture.
Particularly for developing countries, the urban mobility system design based on CPS technology needs to consider some aspects, high number of non-employees, poverty of the populations, local digital innovations (drone cameras), and environmental protection.
Thus, Table 5 presents an overview of the work that highlights the distinctive elements between the urban environments of developed countries and developing countries. Table 5 clearly shows developing countries under a delay in the use of new technologies, and a complex socioeconomic context. Therefore, developed countries have already been anchored in new technologies for a decade. Their urban environment is almost completely digital. Today, these types of countries are rather in the optimal choice of the best innovative technology. Unfortunately, in developing countries, CPUMS development will encounter challenges, as • Position location. The location of households and connected devices in urban environment is an NP-hard problem in developing countries (Rossit et al., 2022). Georeferencing is almost non-existent, apart from internet users who are rarely used Google Map solution. Localization is important for the emergence and recommendation services by human mobility. • Management of interactions to avoid emerging situations. • Optimal deployment of computational devices with better coverage in an unreferenced space. • The management of exchanges between connected mobile agents and the protection of its exchanges against cybernetic attacks knowing that developing countries are poorly equipped. • Managing the collection and processing of the urban Big Data. • The multi-objective process model's formulation for decision support for decision makers.
And also, the solutions proposed must be light and less costly in order to respond to the economic, financial and technological barriers faced by these countries.

CONCLUSION AND PeRSPeCTIVeS
In this paper, a review of the state of the art in the design of sustainable urban mobility systems was conducted. A literature search method integrating database search and related journal search was proposed to select all relevant articles. Based on the selected main articles, the cyber-physical urban mobility system was reviewed, and some related works focusing on sector analysis approaches were presented as well as the design of intelligent transport architecture in the literature. In addition, a comparative study of the concepts applied in developed and developing countries was performed. Based on the local context of developing countries, we have proposed an architectural framework of cyber-physical urban mobility system. A synoptic table of the CPS conceptualization presented helped us to formalize the meaning of each concept in terms of its acronym, constituents, objectives, and identified open problems. Finally, the challenges and open issues of the contribution of cyberphysical systems in urban mobility in the context of developing countries were presented. In view of the upcoming development of an integrated and flexible urban mobility system in developing countries, limitations and perspectives were presented. Future work will cover three main aspects, (1) verification of validation proposal cyber-physical architecture of urban mobility system, (2) developing optimization performance processes to real-time intersections management, and (3) verifying correctness of our model with real mobility data in the context developing countries.