A Review of the Public Transport Services Based on the Blockchain Technology

Abstract

This paper presents a comprehensive review of the technical aspects and challenges in existing public transport services. This review highlights the challenges and solutions for the main subsystems of public transport services, being focused on the influence of public transportation in an urban area with high demographics to identify solutions based on blockchain technology for future development of the current management platforms. More than 2000 research papers, published since 2018 and until now, have been analyzed in Web of Science, Scopus, and ScienceDirect. The keywords used for the analysis of blockchain integration in public transport are related to technology, services, management, the use of electric vehicles, and the impact of public transport on the environment. In this research, we analyzed why there is a need for integrating the blockchain technologies in public transport.

1. Introduction

There is a need for research in the field of public transport that incorporates old and future systems in order to promote economic development, green the environment, decongest traffic in high-demographic localities, and determine the population for frequent use of public transport [1,2,3]. At the same time, it is proposed to improve the car fleet of passenger transport operators by purchasing electric buses [4,5].

In order to develop intelligently, a city must solve, among other things, the problem of traffic [3,6,7]. By traffic, we mean assigning a total role in the transport capacity of the road network, improving traffic safety, solving problems that arise, and prioritizing environmental protection [8,9]. A new technology that allows the use of data in a distributed way, with a high confidence in its manipulation, is blockchain technology, as shown in [10]; thus, allowing the use of another technology different from the ones used so far, which leads to public transport [8].

Blockchain has the ability to solve the management of business data processes and, of course, the management of trading. If the mobility of goods should be studied more intensely, why not apply this to people? Therefore, we need a digital structure that includes the cloud, payment systems, and information management in order to remodel an urban city into a whole new smart city. In the field of public passenger transport, blockchain is in the early stages of research and it is vaguely debated. To date, studies have been conducted in the area of traffic safety and blockchain data sharing [11], as well as the sale of electricity to power electric cars [12,13]. Research in blockchain technology was applied in a single direction by a single user, and now there is the problem of the collaboration of several public users [14].

Cities must ensure the easiest and fastest accessibility of the services offered to their residents and become cleaner to ensure a high quality of life. The public transport service is one of the services that significantly influence these aspects. In order to make urban mobility more sustainable, public transport is the main component that should be improved. Certain shortfalls can lead to an increase in external costs due to pollution, inefficient time management, and other elements that can influence people’s professional and private lives.

In order to obtain an image of the traffic situation in big cities, it is also important to collect data on the flow of mobility in the area. Sustainable mobility architecture will have to be created with the use of concrete data and with ecological machines that reduce emissions and save space, time, and energy.

Therefore, the external costs accumulated by public transport (noise, pollution, expropriations, infrastructure work, etc.) that contribute to the price of public transport must be removed. Along with these previously mentioned aspects, the awareness of users is important. By choosing this type of mobility through the use of electric (ecological) vehicles, which are less harmful to the environment, for public transport, the accessibility and attractiveness of routes and the organization of traffic can be improved. All of these features allow users to take into account the common good when choosing their means of transportation.

The public transport systems in different countries are different from each other and the representative characteristics of some transport systems are detailed below.

Germany: Twenty-five or thirty years ago, traveling from one end of Germany to the other meant a paper ticket and separate fares. We never would have thought of doing all that work and do not even imagine buying a paper ticket now. Today, we live in a digital world where people will finalize their travel plans online [15].

Russia: Intelligent traffic through real-time lane sharing is available. It is possible to share lane space with other vehicles traveling on the same route by bartering using blockchain technology with other private car owners [16].

America and Canada: In these countries, the focus is on exchanging, storing, and publishing data using application programming interfaces (APIs) [17].

Latin America: Transport providers are excited about the potential for blockchain to provide decentralized transaction systems. These systems can allow for increased coordination and trust without the intervention of an authority [17].

São Paulo and Rio de Janeiro: the public transport system accepts credit and debit network payments; travelers can also pay their fares using bitcoin [17].

Hong Kong: The MTR Corporation has already committed to developing a viable blockchain product with some of its spare parts and equipment suppliers using blockchain-based contracts. This is a blockchain application development process, where orders are triggered when stocks drop below a threshold and the supplier is ready for receipt of spare parts [17].

Brazil: The city of Teresina created the “Observatório do Transporte” (the Transport Observatory) and collaborated with the French Economic Development Agency (AFD) through EUROCLIMA (a program to launch a transport technology innovation project) [17].

The major problems in public transport services are as follows:

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Dealing with the issue of urban congestion;

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Greenhouse gas emissions;

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A lack of integration between public transport services and technology;

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Fraud and security.

The goal of this mapping study (following the guidelines in [18,19]) is to determine why blockchain technology must be integrated in public transport.

Public transport services play an important role in the transformation process of big urban cities, which must decrease CO₂ emissions and also must improve the citizens’ quality of life. A solution to resolve all of these problems is to integrate blockchain technology into public transport services, public transport technology, the public transport environment, public transport management, and electric vehicles. In this context, using the works published from 2018 until now in Web of Science (WOS), Scopus, and ScienceDirect, a bibliometric analysis map was made based on the PRISMA methodology [20,21], considering the following keywords: public transport technology, public transport services, public transport environment, public transport management, and public transport electric vehicles. Papers that mentioned blockchain technology were identified using keywords mentioned in the search in WOS, Scopus, and ScienceDirect. The publication statistics on these databases are shown in Figure 1.

Figure 1. Trend analysis for keyword searches in WOS (top), Scopus (middle), and ScienceDirect (bottom). A comparison of this review with other reviews published in the last five years about blockchain for public transport services is made in

Table 1. Existing reviews on blockchain for public transport services.

Reference		Blockchain from Public Transport Services Perspective				Public Transport Services Considered
	Objectives	Technical Issues	Environmental Impact	Security	Challenges and Solutions	EVs	PTT	PTS	PTE	PTM
[1]	✓	✓	✕	✓	✓	✓	✕	✓	✕	✓
[2]	✓	✓	✓	✓	✓	✓	✓	✕	✓	✓
[3]	✓	✓	✕	✓	✓	✓	✓	✓	✕	✕
[4]	✓	✓	✕	✓	✓	✓	✓	✕	✕	✕
[5]	✓	✓	✕	✓	✓	✓	✓	✓	✕	✓
[6]	✓	✓	✓	✓	✓	✓	✕	✓	✓	✓
[7]	✓	✓	✕	✓	✓	✕	✕	✕	✕	✕
[8]	✓	✓	✕	✓	✓	✕	✓	✓	✕	✓
This survey	✓	✓	✓	✓	✓	✓	✓	✓	✓	✓

(where the symbols ✓ and ✕ mean that the problem is analyzed, or not, respectively).

Figure 1. Trend analysis for keyword searches in WOS (top), Scopus (middle), and ScienceDirect (bottom). A comparison of this review with other reviews published in the last five years about blockchain for public transport services is made in Table 1 (where the symbols ✓ and ✕ mean that the problem is analyzed, or not, respectively).

Thus, the main contributions of this paper are as follows:

➢

An overview of problems in existing public transport services is presented;

➢

This review highlights the state-of-the-art of public transport services using bibliometric maps using the WOS, Scopus, and ScienceDirect databases;

➢

This review focuses on the influence of public transportation in an urban area with large populations to propose solutions using blockchain technology for future development of the current management platforms;

➢

This review focuses on public transport management using blockchain technology that is analyzed from a sustainability point of view related to environmental, economic and social, and public awareness effects;

➢

Results obtained using blockchain technology are associated with each identified keyword.

Future research directions are presented and critically discussed, highlighting the implementation stage for each new concept in the literature.

The novelty of this research is in the future research directions provided by the bibliometric maps, which highlight the trends from the WOS, Scopus, and ScienceDirect databases. This bibliometric map helps the researcher see the state-of-the-art for the new research directions.

The paper is divided into an introduction and five other sections, as detailed in Figure 2.

Some concepts and definitions from the literature used in this paper are presented below:

Distributed Ledger Technology: “DLT is a virtual decentralized database or ledger, often encrypted for security, maintaining a permanent and tamper-proof record of transactional data. It is managed by computers allowing a peer-to-peer (P2P) network, whereby each of the peers (computers) in the network maintain a copy of the ledger.”

Blockchain: “One key difference between a typical data base and a blockchain is how the data is structured. These blocks are then connected, forming a chain of data known as a blockchain. There are other examples of cryptocurrencies and open or closed platforms of which dedicated blockchain applications can be created.”

TechTarget: “Each of the computers in the distributed network maintains a copy of the ledger to prevent a single point of failure (SPOF) and all copies are updated and validated simultaneously.”

Gartner: “A blockchain is an expanding list of cryptographically signed, irrevocable transactional records shared by all participants in a network. A blockchain is one architectural design of the broader concept of distributed ledgers.”

International Transport Forum: “These applications allow agents to enter into direct relationships with each other according to a commonly agreed set of rules and a high degree of trust without having to go through a central authority.”

Thus, blockchain allows “a trusted central platform with rules-based access to individual operators but data can also be utilised by algorithms to provide a common journey planning platform to customers” [17].

2. State-of-the-Art in Related Works

2.1. Blockchain for Public Transport Management

In [22], the paper presents a blockchain-based method of marketing electricity between electric cars located in a certain geographical area with the main goal that aims for a possible solution in order to solve the range issue for electric vehicles. The method in this paper proposes a power trading model with a consortium blockchain to support it and a proof-of-stake (PoS) algorithm instead of the very first used proof-of-work (PoW) algorithm in the blockchain origins. Overall, this method is efficient and feasible with significant cost reduction compared to costs through the traditional power grid trade.

Another model in which vehicle electricity can be traded with peer-to-peer (P2P) transactions through the use of smart contracts and blockchain technology is addressed in [23], where each future member must use a registration form in order to participate in the trading process and furthermore, an anonymous authentication process is required. Results shown in this paper indicate a high-speed process for the proposed model and a secured transaction with data that cannot be changed compared to a transaction in a conventional system.

In [24], the authors propose a blockchain-based EV trading platform that allows smart loading flexibility in order to maintain balance in the energy distribution area. The flexibility is seen in terms of the power and charging time of the electric vehicles, which are traded through this platform. The simulations performed with the proposed platform showed a 50% increase in the use of electric vehicles via this system compared to a normal charging system.

Moreover, Ref. [25] presents an efficient solution for the commercialization of V2V (Vehicle to Vehicle) technologies and V2G (Vehicle to Grid) energy, where the security is achieved through the consortium blockchain, and the payment is made via a smart contract, with the possibility to receive information about the nearest power supply for shortening time and respectively low costs. Additionally, the paper proposes two attack models for the solution, with results revealing significant robustness against both of them.

Research in [26] presents a blockchain architecture for energy trading by sharing the charging/discharging of electric cars and regulating the electric charge during peak consumption periods by minimizing the variation of the network load. The paper presents experiments that use cellular automata to verify the feasibility of the V2G system.

In [27], the authors propose the Proof-of-Useful-Work (PoUW) method for secured and validated P2P transactions that use fewer computing resources as an alternative to the old PoW algorithm. The method in this paper shows low energy consumption for the entire process, and in the end, the authors draw some interesting possible uses of blockchain and smart contracts in various fields that must be taken into consideration for future research.

To go further, [28] solves the problem of sharing electric vehicles for charging. Blockchain architecture is proposed for shared loading and high security, with the trading price being set by a smart contract.

In paper [29], environmental protection and the transformation of cities into green ones through the widespread use of electric vehicles is studied. Possibilities of uploading them through a system that uses blockchain by associating several companies are presented. A new smart contract is designed so that the profit of the companies joining the consortium is fair. A model is proposed that uses the mathematical logic of contracts and a new algorithm called Limited Neighborhood Search with Memory (LNSM), making the smart contract more efficient and faster. The study is validated by using real data from a city in China.

In [30] the use of blockchain technology is proposed in order to achieve data communications between vehicles of any kind, but also the possibility of trading energy by using smart contracts for charging and discharging electric cars. This method is presented by validating the duplication of data in the network, and the integrity of the data is achieved by using a digital signature. To solve data security attacks, the method of hiding data in energy trading is used. The authors believe that energy trading and data security through the proposed IoT system of Electric Vehicles (IoEV) is secure and reliable.

To go further, the authors in [31] created an energy trading platform for charging electric cars in a smart city. The owners of the electric cars carry out renewable energy transactions with the local producers at advantageous prices and can plan the charging system with them. The platform is based on smart contracts, and the system was tested at peak hours with high energy consumption in Singapore, a city with high congestion.

Charging electric cars through an anonymous platform and smart contracts is discussed in [32]. In this solution, by combining the use of zero-knowledge proof, ring signature, and K-anonymity methods, the identity and location of the users are kept anonymous.

Ref. [33] studies the consumption of buildings and transport in terms of energy, which represents about 70% of the global final energy consumption. Less than 20% of this is renewable energy. It is proposed to sell green energy made both by private producers who have installed photovoltaic systems or wind turbines on buildings, and by electric cars. Trading is carried out through a blockchain-based platform.

The paper presented in [34] builds a platform for trading electricity with electric cars. The authors establish a model of costs and revenues for electric cars, for which they perform a strategy to join the coalition. They conclude that its operation cost is higher than the operational cost, and when the number of electric vehicles reaches saturation, the cost of charging decreases by 36%, while revenues will increase by 33% of the discharge of electric vehicles, compared to regular trade.

The authors of the paper in [35] propose a private charging system for electric cars, as the existing system of public stations does not satisfy this problem in a city as large as the one chosen for the case study—Shanghai, China.

Ref. [36] proposes the establishment of trust and data security in vehicle networks and requires an update through the blockchain register of vehicle status. The process is carried out in two stages. In the first stage, the degree of confidence of each candidate is calculated by using a bidding algorithm in order to select the trusted miners, and in the second stage, the selection of the corresponding block is used.

A comparative analysis of the published works that discuss this issue is presented in

Table 2. Analysis of the results of studies in the literature–1st part.

Ref.	Domain	Objectives	Results	Technology	Advantages and Opportunities
[22]	Electric vehicles used by urban commuters	V2V energy trading (Vehicle to Vehicle)	The utility and strength of the proposed solution, for the electric vehicles in the consortium, decreases by 36% in terms of charging cost, and the revenues of those who sell energy increases by 33%.	Blockchain	The cost of charging decreases by 36%, and the revenues of those who sell energy increases by 33%.
[23]	Electric vehicle charging	Electricity trading—charging electric vehicles. Smart contract.	Electricity trading model—charging electric vehicles and comparing with the traditional scheme.	Blockchain	Security, trust and efficiency. Execution speed is higher, calculations and execution are slower in time, data cannot be changed. Opportunities to use machine learning and artificial intelligence technologies as one gets closer to the place of loading.
[24]	Electric vehicle charging	Building smart infrastructure.	Loading electric vehicles using a blockchain-based platform.	Blockchain	50% increase in performance compared to the normal charging system. If the charging network needs to be expanded, the costs will be higher than the proposed software solution.
[25]	Energy trading for electric vehicles.	Power supply for electric vehicles in smart city.	V2V and V2G energy marketing; Ethereum Resistance Security models are being studied.	Blockchain	The proposed system is powerful for external attacks, it is validated as high performance. For both V2G and V2V, energy trading is done efficiently.
[26]	Energy trading	V2G (Vehicle to Grid) trading	Building a blockchain architecture. Smart contracts; scheduling the loading and unloading of electric vehicles.	Blockchain; smart contract.	Realization of an experimental trading platform, with the help of which the trading can be validated. Future research will look at the road network, traffic flow and spatial factors that may disrupt the suggested pattern.
[27]	Transportation transactions	Transactions	Track, manage and validate transactions, and optimize transport applications taking advantage of its ecosystem. Model making.	PoUW-based blockchain	Model making and rewarding miners. The proposed method reduces energy consumption.
[28]	Electric vehicle shared charging.	Shared upload architecture.	Fast search, secure storage, computing and incentives.	Blockchain	Increasing the security of the proposed architecture for sharing the load of electric vehicles.
[29]	Electric vehicle charging	Making models, faster and better smart contracts.	A new model of smart contract, validated with real data from Beijing, China.	Blockchain; smart contract.	The proposed mathematical model decreases the complexity of the calculations, which was followed by numerical experiments. For the future, the aim is to research the cross-chain through the blockchain, connecting more data to achieve a smart society.
[30]	Data and energy trading—electric vehicles	Data trading between vehicles. Charging/unloading electric cars by trading energy.	Development of an IoEV that ensures data security and reliability.	Blockchain; smart contract.	Efficient data validation system by removing duplicates, which reduces storage costs. The technique of hiding accounts is used to protect information.
[31]	Electric vehicle charging—smart city	Energy trading architecture.	Energy trading platform from local renewable energy producers with optimal charging planning and at advantageous prices.	Blockchain; smart contracts—on the Ethereum private network.	Testing was performed at peak hours in crowded cities.
[32]	Electric vehicle charging—anonymous	Anonymous charging system for electric cars	Security and anonymity regarding the location and the person.	Blockchain; smart contract.	Use of smart contracts to complete the transaction ensures data security and maintaining confidentiality.
[33]	Buildings, power supply	Grid networks—powering buildings and electric cars.	Green energy trading platform for buildings and electric vehicles.	Blockchain	Go through and present the current stage in the use of blockchain in the sale of existing renewable energy in buildings and electric cars.
[34]	Electric cars. Loading, energy trading	Energy trading.	Energy trading platform.	Blockchain	Decreased charging costs and increased revenues for electric cars that sell electricity compared to the existing system.
[35]	Charging electric vehicles in the city	Case study—charging electric vehicles.	Charging solution platform from private energy producers.	Blockchain	Improving the sharing system for faster charging of electric vehicles.
[36]	Electric vehicle charging	Data security.	Selection of the optimal miner. Miners are selected by calculating data quality, trust and confidentiality.	Blockchain	Compared to the logical approach, the selection rate of the corresponding miner from the malicious one is improved. For the future, the development of the study is aimed at increasing the number of blocks.

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2.2. Blockchain in Public Transport Technology

Case studies for smart communities and application models based on blockchain technology and intelligent communications architectures are presented in many papers. The goal of [8,36] is to use blockchain technology for smart communities. The authors in [37] use IoT to allow traffic vehicles to collect data and pass them on. Vehicles connected to the network will each form a network node. The research is aimed at how to authenticate vehicles via blockchain, and the system security is demonstrated by informal and logical Burrows–Abadi–Needham (BAN) analysis. The correctness of the scheme is simulated through Internet applications. Compared to similarly designed schemes, the authors obtained good results in lightweight characteristics. BAN logic will ensure data security, and in addition to security, it is shown that the performance is higher compared to the existing ones.

Ref. [38] deals with data security in intelligent transport chains using blockchain technology. The proxy algorithm is a re-encryption algorithm that uses the ciphertext-policy attribute that searches for keywords that also share data and send it. Data access is controlled and the communication environment is efficient and secure for random networks. Services such as insurance companies, traffic police and maintenance providers have access to the text in encrypted form. Then, by applying a smart contract, one can offer personalized services after decryption.

Ref. [39] provides a prediction algorithm based on the neural network for the correct determination of the vehicle’s position—GSM. With blockchain, positioning errors are stored in order to guarantee the condition of the vehicle. Additionally, in this paper, an error correction algorithm has been proposed to manage to overcome possible faults or missed predictions.

For local freight networks in [40], a blockchain-based solution is given, keeping in mind that the home delivery trade has developed a lot. Thus, a secure architecture between the parties is presented with the payment mechanism made by smart contracts and the transport route followed by UHF-RFID antennas, while cars are equipped with RFID tags.

A comparative analysis of the published works that discuss this issue is presented in

Table 3. Analysis of the results of studies in the literature–2nd part.

Ref.	Domain	Objectives	Results	Technology	Advantages and Opportunities
[8,36]	Smart communities	Using blockchain technology for smart communities.	Study of the different process methods used for secured transactions.	Blockchain	Detailed presentation of applications, providing support that provides the necessary communications infrastructure for applications.
[37]	Regional vehicle internet authentication	Vehicle Internet (IoV)—IoT application in transportation.	Designing a simple, low-power authentication scheme. In operation on the schema, XOR, hash functions, and symmetric encryption are used. IoV has low resource consumption.	Blockchain	Low resource consumption. The data are collected and will allow the blockchain to record the nodes.
[38]	Communications—intelligent transport	Data security scheme.	Data encryption system. Decryption takes place after verification and the launch of the smart contract.	Blockchain	High security system by encrypting/decrypting traffic information.
[39]	GPS vehicle	Vehicle positioning in the area.	Prediction algorithm based on neural network.	Blockchain	Reduce as much as possible the errors caused by the fact that some of the vehicles are equipped with data sensors and others do not have such equipment, and for this reason there are errors in indicating the position of the vehicle at a given time.
[40]	Intelligent freight transport	Solution developed for local freight networks.	Smart contracts based on Ethereum.	Blockchain REF, IoT	Data privacy. Smart contract trading. Track parcel route (location) during transport.

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2.3. Blockchain Used in Public Transport Services

This section analyzes the solutions proposed in the literature for parking lots, the detection of false traffic announcements, the reduction of pollution, the optimal charging of electric cars, the confidentiality of data, methods to stimulate smart urban transport, etc.

Ref. [41] proposes the collection of data from vehicle-mounted IoT devices and road infrastructure in the nodes called Full-Nodes. The sensors in the network record various data such as Global Positioning System, air quality control, and speed camera data in the locality. The proposed system solves some of the problems of congested traffic and parking. In order to overcome these problems, the small processing power of the existing IoT devices and the lack of IoT devices for urban transport were found.

The method of transport in Ref. [42] is the maritime one, where its security and management are pursued. The use of blockchain technology, found by the authors, brings increased security and elimination of fraud, shortens the response time of containers, shortens the downtime of ships, reduces carbon emissions, and allows transparent data exchange.

In Ref. [43], the way in which confidentiality and security concerns are managed in the transport systems is researched. In this work, with the help of blockchain technology, the communication system between vehicles is realized. The blockchain investigates trust management, and the problems detected by false messages are highlighted by identifying the node that claims the message.

Ref. [44] deals with identity management issues in terms of public transportation and proposes a decentralized system or to use the same public travel card in multiple areas. The blockchain establishes the identity of the vehicles and the transport management that takes place in several countries with operators that provide different types of transport.

The authors in [45] analyze an energy-secure parking lot located at a short distance from the vehicle’s positioning in space at a given time.

In [46], the authors state that 45% of CO₂ emissions come from buses, motorcycles, and taxis. To reduce pollution, they propose the use of electric cars. A platform is created where the process is followed by the QR codes of each transport.

Flexibility and fault tolerance are studied in Ref. [47]. Due to the different densities of the vehicles, the membership takes into account joining a blockchain group. The paper proposes a block scheme that helps choose the best partners, taking into consideration the density of vehicles. Multiple blockchain channels are defined, and each of them is optimized according to the destination of the vehicles. The platform will select the optimal channel according to the density, requirements, and latency of the transaction. Through the simulations performed in this paper, results showed that the proposed scheme performs better than the existing one.

Ref. [48] deals with the confidentiality of data in the communications system regarding the location, means of transport, and identity that are anchored in traffic. This paper proposes a scheme to improve these issues regarding data privacy attacks. Pseudonyms are used, with a frequency of reuse and the amount of their consumption, from the transmission networks, reducing the generation costs. When mixing pseudonyms, the proposed scheme gives better results than the existing one.

Ref. [49] provides a way to stimulate traffic. Messages given and received from traffic must provide credibility. To stimulate those who offer correct messages, a stimulation system called SmartCoin is proposed. A scheme is proposed, and it offers social security, improved transport, decongesting traffic, reduced road accidents, and a safe, fraud-free transport network. The redemption of the virtual currency can be done at the filling station, at the electric charging station in the case of electric vehicles, or at the service. Through this scheme, the time for consensus is decreased by 90% and the costs for communication and storage are lowered by 70–80% compared to the existing schemes.

Ref. [50] makes a comparison between the proposed solution using 5G and B5G technology and the one that is approached today based on the cloud in iFogSim for traffic decongestion. Blockchain technology is proposed to be used in order to increase performance through a customized implementation. From the simulations performed, it is stated by the authors that superior results were obtained.

Ref. [51] presents a series of applications that use blockchain technology in the field of transport, logistics, and supply chains for trading, with the advantage of preventing traffic congestion. The proposed platform, in addition to the ones shown above, allowed a dynamic of taxes, in case of emergency giving priority, and a lane for trucks and towed vehicles. The proposed mathematical model analyzes the charging scheme of tolls for congested traffic in urban areas.

The safety of special transports, such as the transport of heritage objects and very large equipment, refers to the protection against damage that may occur during transport. A solution to improve the transport and protect the heritage objects of museums in the process of cooperation and knowledge sharing is proposed in [52]. IoT and blockchain are proposed for transporting old objects (which are part of the cultural heritage). Changing environmental and climate conditions, as well as location, are monitored in real-time from a distance.

In [53], the possibility of problems in the application of blockchain technology to achieve mobility in the real world is discussed. A risk assessment framework for the case study is proposed to quantify it. The analysis is performed in three stages: establishing the participants in the study, analyzing scenarios that may cause problems, and a combined analysis to determine the increased risks and the impact they bring in terms of finances, confidentiality, trust, and integrity of those concerned.

A comparative analysis of the published works that discuss this issue is presented in

Table 4. Analysis of the results of studies in the literature–3rd part.

Ref.	Domain	Objectives	Results	Technology	Advantages and Opportunities
[41]	Smart urban transport	Distributed network—urban transport.	A distributed network for collecting data from sensors in the equipment: vehicles, road infrastructure, vehicle congestion check.	Blockchain, IoT	A network distributed with sensors from a locality. Data are collected from both moving and parked vehicles from the atmosphere. They are stored in nodes that in turn communicate with each other.
[42]	Port operations and maritime transport management	Applications and architectures.	Solutions for the use of blockchain in maritime logistics	Blockchain	Discussed applications and proposals of private architects (Hyperledger Fabric and Hyperledger Besu) to show their importance in port activity.
[43]	Communication between vehicles	Detect node that emits false messages.	Security and message fidelity.	Blockchain	Identify fake messages.
[44]	International passenger transport	International transport management.	Self-sovereign identity is applied in public transport management for economic operators in several countries.	Blockchain	The system analyzes how the single travel card is used for all travel providers. It is a concept by which a person better manages identity credentials through self-sovereign identity.
[45]	Smart parking	Secure and fast parking system.	Smart parking in smart cities, privacy.	Blockchain	Offering drivers the opportunity to park their cars in the right place.
[46]	Electric vehicles	CO2 pollution reduction	Sandbox blockchain translation simulation platform. Ethereum.	Blockchain	A platform with a mobile/desktop application has been developed. Supervision is done using the QR code.
[47]	Vehicle internet—management	Optimal loading group adherence scheme.	When doing so, take into account the number of vehicles in the area.	Blockchain	The best choice for trading by joining a block.
[48]	Economic confidentiality—intelligent transport system	System for maintaining data confidentiality.	Self-defense measures are taken by the proposed system.	Blockchain	The proposed scheme was evaluated with superior performance in terms of the number of pseudonyms that are mixed.
[49]	Public transport	Stimulating smart vehicles. Traffic improvement—message generation.	The scheme is superior to the existing one. Drivers are stimulated by virtual currency to provide accurate information.	Blockchain	This technology helps to store the correct data and asses the confidentiality of correct data and respectively to stimulate the people who contribute to the creation of a correct information base.
[50]	Traffic decongestion	Solution offered in order to decongest the traffic and pollute the environment in the locality.	Achieving better results than using current technologies.	Cloud Intelligent Vehicles and Vehicle Ad hoc NETwork (VANET), Blockchain 5G and B5G	Cloud computing, enhanced with blockchain and fog computing, allows to improve latency performance and scalability and avoid traffic jams by tracking the location of the vehicle.
[51]	Transport—traffic decongestion	Traffic decongestion	A platform for setting tolls, prioritizing emergencies, and transporting heavy trucks and towed vehicles.	Blockchain	Fast and clearly superior results, but the amount of information grows exponentially, so in the future, the use of Big Data will be considered.
[52]	Transport	Culture protection—museums; object distribution and knowledge sharing.	Real-time monitoring, with high security of exhibits from one museum to another through the combined support of IoT and blockchain.	Blockchain, IoT	Real-time tracking of the transport of museum objects, without incident, with high security.
[53]	Smart mobility	Security; assessing the risks of cyber-attacks in mobility/transport.	Three-stage analysis: establishing study participants, analyzing scenarios that may cause problems, and a combined analysis to determine the increased risks and impact they bring from a financial, confidential, trustworthy, and integrity level.	Publicly authorized blockchain	The larger the false information, the more vulnerabilities are introduced into the system. In future works, it is desired to bring concrete solutions to achieve these problems.

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Together with the reduction of the external costs of public transport, we can also talk about promoting the decarbonization of mobility. Pollution, road traffic congestion, noise, accidents and suboptimal use of space have an influence on the quality of life and health of the population. Due to the increased importance of sustainable and intelligent mobility of people, it is necessary to introduce innovative mechanisms through the use of new technologies such as blockchain. This technology is successfully used to ensure security in the storage and collection of data that identify the flow of traffic mobility in large cities. The attractiveness of this form of transport for peopled will increase through a series of advantages such as availability, frequency, passenger transport connections, and price.

The application of blockchain technology allows tracking and directing the movement of vehicles used for public transport to routes with a low risk of collision and areas with the efficient use of space, leading to a reduction of external transport costs.

Thanks to the blockchain technology, which allows a strict monitoring of the transport of people, the result is a maximization of benefits, but also a reduction of social costs.

3. Public Transport Services and the Environment

3.1. The Influence of Public Transport on the Environment

In the European Union (EU), 30% of carbon dioxide emissions come from transport [54,55]. From this percentage, road transport takes an increased credit of 72%. This percentage is expected to be reduced by 60% in 2050, taking into consideration the emissions in the early 1990s, although the percentage is rising every year. A significant contribution comes from the transport of people, which in most cases is done with a personal car. The more people travel, the more pollution will increase, as can be seen in Figure 3. It should be noted in Figure 3 that the percentage of CO₂ emissions for road transport is separated by category: cars, big trucks, small trucks, and motorcycles.

Recent studies have shown that the worst pollution is recorded in public passenger transport. This is influenced by the type of means of transport. About 60.7% of the amount of carbon dioxide (CO₂) emissions in Europe comes from private cars. An improvement to the situation would be for public transport to be used by more people; in this way the traffic will decrease, as well as CO₂ emissions. Regarding the flow of people transported by cars in traffic, a calculation was made in Europe, and a value of 1.7 people per car was obtained [56]. In order to reduce CO₂ emissions, it is necessary for the efficiency of the cars to increase or for them to be supplied with clean fuel. Today cars are generally powered by gasoline or diesel. When calculating the CO₂ emissions of a car, these emissions are summed up, including those when using the car and those that are obtained due to the production of fuels. With the intensification of renewable energy production, the problem of using electric cars arises (see Figure 4).

Although during production, electric cars are more harmful, the emissions produced during manufacturing are compensated for as electric cars are less polluting than cars that run on gasoline or diesel engines.

However, given the average energy mix in Europe, electric-powered cars are proving to be cleaner than petrol-powered vehicles. As the share of electricity from renewable sources increases in the future, electric cars will become less and less dangerous to the environment.

As of 1 January 2020, the EU regulation on CO₂ emission standards has been applied to new cars and low-capacity cars (vans) [57]. In this regulation, in the period of 2022–2030, methods are proposed to stimulate those who meet these conditions.

These measures are currently in progress, and the effects are not yet visible.

Ref. [58] investigates how local and government authorities can take action to improve public transport for passengers in order to get them to use such transport, thus helping to reduce environmental polarization.

In [59], research was carried out in the field of maritime transport. By using blockchain technology, the documents used for transport are no longer obtained using paper support; instead, electronic support is used to store and transmit information. Starting from this argument, we apply the idea of public transport. If only public passenger transport is analyzed and the concept is applied, there will be a decrease in environmental emissions from paper. Blockchain technology offers the ability for information to be stored electronically in a secured manner.

Ref. [60] starts from the reduction of greenhouse gases until 2050, as agreed upon in the Paris Convention. It is proposed to stimulate and respectively pay a CO₂ emission tax proportional to energy consumption. The research proposes a distributed register that analyzes the technological requirements.

3.2. Public Transport Management

The movement of goods and people is a defining element of today’s society, which has experienced unprecedented growth in recent years. Thus, there is an acceleration of undesirable effects due to transport, for both human health and the environment.

3.2.1. Public Transport Management—The State of the Art

A person’s mobility arises from an individual’s desire to move between two points [61,62]. In order to realize this desire, the best method must be accessed, taking into account an efficient reputation in this respect. When making a decision, we must take into account either the means of transport we have or the conditions in which the travel is made, the reservation, and the coordination of the payment of the services.

In this sense, the paper in [62] analyzes the challenges that influence mobility, choosing Lisbon as a case study. The study treats the challenges involved in the process of current mobility of home–work–home, home–school–home, etc., carrying out the transport planning being done later with a traditionally used method: forecast–plan–delivery. By using the sharing principle, the paper proposes the development of Mobility-as-a-Service (MaaS), and through this, public transport becomes a commodity to which the IoT applies. Today, all of the events take place in a permanent competition where the winners are not known, and there is no goal so far to reduce the use of cars for people’s mobility. If we consider the recent problems (the COVID-19 crisis), these problems have become even more pronounced.

In [63], the similarities and differences between the MaaS concept and another concept called the Mobility on Demand (MOD) are discussed. There are two different concepts, one refers to mobility as a MaaS service, and MOD refers to mobility on demand. These concepts have aroused interest, so in [64] the advantages and disadvantages of these concepts that are applied in different countries are analyzed. The commercialization of passenger mobility as a whole with the transport and delivery of goods are defining elements for MOD, while the aggregation of passenger mobility and subscription services characterizes MaaS. The public sector has a major contribution to their development, which can take the form of partnerships, information, pricing, and so on.

The car industry marked a great development favoring the increase of the number of cars on private property within a family and, at the same time, the increase of their number in traffic, especially within the localities with a high population density. Within a crowded urban locality, the trips made on foot or by using bicycles or scooters are not enough if we take into consideration the number of inhabitants in the area.

With an increasing number of users of personal vehicles, the road area is inadequate; it is usually too narrow or unable to be modernized due to the buildable space. The fastest option would be to use public transportation, but this kind of concept is often considered by most people as a poor alternative. Such mobility is perceived as such because it currently offers inadequate and undesirable transport conditions and congestion, especially during peak hours, and therefore travel within inappropriate conditions. The frequency of busses’ arrival at waiting stations, the slow speed of the vehicle due to traffic congestion, and the delay in arriving at passengers’ destination are other disadvantages that contribute to the choice of such a possibility for passenger mobility.

Surveys conducted among the passengers highlighted the desire and choice of their personal cars.

In modern society, possessing and driving a car means liberty, but no one thinks about the impact and damage to the environment over time. This has led to environmental, social, economic, and passenger safety issues.

The vast majority of vehicles currently in use produce toxic emissions that, over time, can cause global warming and can generate acid rain.

In order to produce some changes, first of all, the passengers’ vision must be enlarged, working on both their mental and psychical sides but also on the material side, in order to encourage them to use different ecological means of transport more often.

The studies carried out in [65] aimed at controlling the demand for public transport, in terms of the loading capacity of public transport, especially during the period when social distancing protocols were imposed during COVID-19. In the paper, the passengers who wanted to travel for a period of time were constituted in models where about 90% of them travel a strict and direct route every day that allows programming and coordination of the space in the bus and also, while waiting, stations can be coordinated. The transport operators, in agreement with the local administration—the mayor’s office—made a map of the analyzed area regarding the place of residence, work, study, and interest in public and private services. Thus, a mobile application was proposed that can organize and synchronize in real time the arrival time of the bus, the stops, and the time for the passengers to arrive at the station, all being done according to the capacity of the means of transport regardless of the external environment (with a pandemic or not). The application can provide information taking into account the fluctuation of passengers, namely: day of the week, school holidays, and days off. The research was focused on a single passenger transport line and did not take into account the fares and the possibility of travel by other means.

Ref. [66] analyzes the public transport challenges and opportunities in various parts of the world. This analysis can result from a series of problems that may arise in the amalgamation of public transport, as can be seen in Figure 5, and all of these problems can be summarized with the statement that the European public transport operators have satisfactory stability in terms of efficiency. The study showed that this score was influenced by the number of family members, the unemployment rate, and owning a personal car. At the antipole of land-based transport is the transport made with the subway, which is more frequented by students. Policies to support public bus transportation increase the quality of life in the community and offer the possibility of selecting a partner for passenger transportation. Public transport is also influenced by the demographics in the area, unequal revenues, and the way the public network was built, as well as the way in which contracts are made. The analysis performed in the research [67] was limited to a small number of years analyzed due to a lack of data.

In [68], research carried out on a smart city proposed smart management for public transport, which is a political priority. The authors offered to support the authorities in making decisions regarding public transport in the locality. A way to prioritize the movement of buses on special lanes was proposed. In this way, the movement is made in a shorter time, and a linear model is applied depending on the speed of the means of transport for time and space management. The application was tested in the city of Porto, giving good results, taking into account two variables: special bus lanes and space priority.

Furthermore, Ref. [69] analyzed the health of the population influenced by public transport, which must be improved. Planned behavior and surveys conducted online to observe the dependence of psychic factors on public transport are two methods used in this paper. The survey was conducted in Beijing, China.

The problems that arise in terms of the tram station in a locality are oriented towards:

(a)

Problems related to people:

While the number of cars is increasing, problems that occur often include:

➢

Improving the road infrastructure to the disadvantage of the natural habitat areas;

➢

The quality of life has been changed by the presence of noise, harmful gases in the air, and traffic accidents;

➢

The pedestrian and play area is reduced, as well as the possibility of building cycling tracks.

(b)

Problems with the car:

➢

Increased noise due to continuously increased motorized traffic;

➢

Reducing traffic congestion will influence environmental conditions;

➢

Convincing people to drive in certain places or at certain times by offering rewards;

➢

Establishing government regulations to use other means of transport such as car sharing;

➢

Generating laws that encourage the use of environmentally friendly and safer cars.

(c)

Environmental issues:

Air and climate quality are also influenced by the use of fossil fuels in transportation.

• In this sense, we can mention:

➢

CO₂-containing exhaust gases;

➢

Nitrogen oxides and suspended particles;

➢

The main source of the noise.

There is the problem of reducing pollution through the more intense use of public transport, and at the same time, there is the problem of improving transport conditions by replacing old and inadequate means of transport with electric cars.

Renovating car parks with electric cars in mind will reduce the overall level of greenhouse gas emissions and air pollution, especially if the electricity comes from renewable sources.

3.2.2. Public Transport Management Proposed Using Blockchain Technology

We live in an age where technology has become indispensable to our lives, advancing so far that it is found everywhere. The advantages of technology are many for mankind, but each advantage can become a disadvantage at the same time. Technology tempts us to publish our personal statements and facts online, where they seem safe, but in reality they are not. Technology allows malicious people to steal them, which should be difficult, and yet it is actually quite easy. This leads to identity theft and unauthorized access to bank accounts or other Internet accounts.

With this in mind, this study provides a self-administered digital identity security system.

Users can create a single digital identity with which they can register on different web platforms by scanning a QR code using their mobile phones. This allows the individual to access multiple user accounts without the need for a password. The user’s digital identity will be stored in encrypted form in the blockchain, thus ensuring its security.

A blockchain is an expanding list of records, the so-called blocks, that are combined together using cryptographic methods and algorithms. Each block is formed from a cryptographic hash of the previous block, a timestamp, and transaction data that are usually represented with the Merkle tree method. The timestamp reveals that the transaction data existed when the block was published to enter its hash. Because each block contains information about the previous block, a chain is built, with each additional block strengthening the ones before it. Therefore, blockchains are resistant to changing their data because once registered, the data in a particular block cannot be altered retroactively without altering all of the blocks before.

Blockchains are usually managed by a peer-to-peer network for use as a public distributed register, in which nodes collectively adhere to a protocol to communicate and validate new blocks.

A blockchain is a decentralized and distributed public digital register of records called blocks, which is used to record transactions on multiple computers so that any block involved cannot be changed retroactively without changing all of the blocks before. This allows users to verify and audit transactions independently and at a reasonable price. A blockchain database is managed autonomously using a peer-to-peer network and a distributed timestamping server. They are authenticated by mass collaboration fueled by collective self-interests; such a design facilitates a robust workflow where participants’ uncertainty about data security is marginal. Using a blockchain eliminates the infinite reproducibility feature of a digital asset. This indicates the fact that each unit of value has been transferred only once, solving the long-term problem of double spending. A blockchain has been described as a value exchange protocol. A blockchain can retain title rights because, when properly configured to detail the exchange agreement, it provides a record that requires bid and acceptance.

Trade or business exchanges between anonymous parties without the need for an intermediary lead to a smart contract. The smart contract contributes to the realization of transactions between the parties as in [70,71,72].

In [8], the authors make an analysis from an economic, social, and environmental point of view, managed with the help of blockchain technology.

• Economic

According to [8], the cost is analyzed from the point of view of:

-

Transaction;

-

Management;

-

Infrastructure construction;

-

Finance.

The blockchain transaction history is strong and permanently stored. The registries are so reliable that the costs are low. Through smart contracts, trust between the parties will increase during the transaction. This new distributed and decentralized system leads to reduced costs by removing intermediaries. According to researchers in [18,19], results show lower transaction costs. Discounts are also recorded by the management and from the data loading process as a measure for the elimination of fraud in their surveillance system.

Significant reductions are made through the use of paperless contract using on-time contracts through shared databases, as in [62].

By using the blockchain, information is obtained regarding the traffic, its structure in the areas with heavy traffic, the restoration of parts of the roads, and the location of bus stations, so that overall, there is an improvement of the road infrastructure [8]. From a fiscal point of view, blockchain technology contributes to the decrease of fraud, allowing to follow the profile and the tax of companies [8].

In [67], the economic importance of using blockchain technology in public administration is emphasized. The study shows the importance of applying this technology at the level of government agencies in different layers, taking into account international experience. When applying this technology, advantages are obtained by reducing costs, immutability, reducing the risk of documents being lost, eliminating intermediaries, distributed stored information, security, trust, the violation of constitutional rights, etc.

2.

Social and Public Awareness

Today there are more and more debates about smart cities, and along with other objectives, smart transport is expected in a smart city. The research in [70] deals with just that, solving inefficient mobility that leads to traffic congestion problems that frustrate residents and lower the quality of life. Another problem is CO₂ emissions; hence the need for sustainable mobility concepts where blockchain technology is used in travel sharing, electric charging, managing block interactions, or communication between vehicles.

The large mass of people owning personal means of transport will be the ones to be persuaded to use public transport to the detriment of personal transport.

Blockchain technology can have substantial support in this direction. Blockchain registries are immutable and permanent, and they are suitable for publicly consumable information.

Hence, blockchain could help to get started:

-

Travel sharing;

-

Dissemination of critical data—in the sense that if a bus cannot reach the station due to technical problems, one cannot reach the destination (work especially) on time;

-

Creating more efficient ticketing systems (it is hoped that purchasing and applying for public transport tickets could become easier—people should not have to buy tickets from different locations during the commute—these systems can be replaced by digital platforms);

-

A platform to keep records and perform transactions;

-

A digital system for tickets, receipts, confirmations, and other aspects of the trip will reduce the hassle, such as the lack of a subscription to a possible check—valid for both commuters and passengers.

The blockchain can be thought of as attractive to riders, who may receive various rewards when using such transport other than the traditional way of traveling [71].

3.

Environmental

Environmental protection is an important directive pursued in the process of public transport. In this sense, in addition to decongesting traffic, a solution is to force people to use buses instead of their own cars. For the people who are from outside the locality, it is recommended to park the cars in parking areas especially arranged on the outskirts of the cities near the roads at the entrance to the locality, and to use public transport within the locality. The warehouses of goods will be located outside the locality so that the vehicles that make the supply will no longer enter the territory of the locality. In this way, the traffic is decongested in the locality, and at the same time, the gas emissions will be reduced, and thus the environment is protected and the air is cleaner. Gradually, the transport inside the locality will be achieved with non-polluting means, possibly powered by electricity.

In [10] there is an example of public transport in Hamburg, Germany, that can be used in the future through a network of buses that have charging systems for electric buses. These stations will be able to charge buses from various manufacturers and thus will solve some of the non-polluting transport requirements in smart cities.

The first problem to be solved would be in the direction of maintaining the fleet. Then there would be improvements in terms of:

-

A 8.7% lower consumption for high-performance buses in terms of energy per passenger per mile than using the personal car;

-

A total of 20% less carbon monoxide emissions per passenger than personal vehicles (single passenger);

-

A total of 10% fewer hydrocarbons per passenger.

4. Materials, Methods and Results

Based on the published articles, we used the PRISMA methodology for selected primary keywords such as public transport technology, public transport services, public transport environmental, public transport management, public transport electric vehicle, and blockchain.

In the research, we used the WOS (Clarivate Analytics, Philadelphia, PA, USA), Scopus (Elsevier, Amsterdam, The Netherlands), and ScienceDirect (Elsevier, Amsterdam, The Netherlands) databases.

4.1. Google Trend Analysis

The timeline is August 2018–2022, hence covering all possible searches on the topic. The research was carried out according to the keywords mentioned above (Figure 6). As can be seen from the figure, the maximum search potential was obtained for public transport services. If the keyword blockchain is entered in the search process (see Figure 7b) together with the other specified keywords (except public transport technology), it can be seen that there is no research in this direction of blockchain application in public transport (see the comparison between the two results in Figure 7a,b). Thus, the research is not focused on blockchain technology.

This analysis allows us to observe that public transport services are followed as a research interest by public transport management in a proportion of 50% compared to the first position, while the other requested research directions are covered by less than 50% or almost not at all.

4.2. Search Strings and Databases Search Results

The research papers were selected from the mentioned databases taking into account the year, language, and field.

Table 5. Search strings.

Search	Engine and Search Strings	Nr. of Papers
WOS	Citation Report: public transport services, (Keyword Plus®) AND public transport technology (Keyword Plus®) AND public transport and the environment (Keyword Plus®) OR public transport management (Keyword Plus®) OR public transport electric vehicles (Keyword Plus®) AND Blockchain (Keyword Plus®) and 2010 or 2012 or 2013 or 2014 or 2015 or 2016 or 2017 (Exclude—Publication Years)	60
	2018–2022 and keywords	42
Scopus	TITLE-ABS-KEY ((public AND transport AND technology), (public AND transport AND services), (public AND transport AND the AND environmental), ((public AND transport AND management))	116
	TITLE-ABS-KEY ((public AND transport AND technology), (public AND transport AND services), (public AND transport AND the AND environmental), ((public AND transport AND management))) AND (EXCLUDE (PUBYEAR, 2017) OR EXCLUDE (PUBYEAR, 2016) OR EXCLUDE (PUBYEAR, 2015) OR EXCLUDE (PUBYEAR, 2014) OR EXCLUDE (PUBYEAR, 2013)) AND (EXCLUDE (PUBYEAR, 2012) OR EXCLUDE (PUBYEAR, 2011) OR EXCLUDE (PUBYEAR, 2010) OR EXCLUDE (PUBYEAR, 2009) OR EXCLUDE (PUBYEAR, 2008)) AND (EXCLUDE (PUBYEAR, 2007) OR EXCLUDE (PUBYEAR, 2006) OR EXCLUDE (PUBYEAR, 2005) OR EXCLUDE (PUBYEAR, 2004) OR EXCLUDE (PUBYEAR, 2003)) AND (EXCLUDE (PUBYEAR, 2002) OR EXCLUDE (PUBYEAR, 1999) OR EXCLUDE (PUBYEAR, 1998) OR EXCLUDE (PUBYEAR, 1997) OR EXCLUDE (PUBYEAR, 1994)) AND (EXCLUDE (PUBYEAR, 1990) OR EXCLUDE (PUBYEAR, 1989))	40
	TITLE-ABS-KEY ((public AND transport AND technology), (public AND transport AND services), (public AND transport AND the AND environmental), ((public AND transport AND management))) AND (EXCLUDE (PUBYEAR, 2017) OR EXCLUDE (PUBYEAR, 2016) OR EXCLUDE (PUBYEAR, 2015) OR EXCLUDE (PUBYEAR, 2014) OR EXCLUDE (PUBYEAR, 2013)) AND (EXCLUDE (PUBYEAR, 2012) OR EXCLUDE (PUBYEAR, 2011) OR EXCLUDE (PUBYEAR, 2010) OR EXCLUDE (PUBYEAR, 2009) OR EXCLUDE (PUBYEAR, 2008)) AND (EXCLUDE (PUBYEAR, 2007) OR EXCLUDE (PUBYEAR, 2006) OR EXCLUDE (PUBYEAR, 2005) OR EXCLUDE (PUBYEAR, 2004) OR EXCLUDE (PUBYEAR, 2003)) AND (EXCLUDE (PUBYEAR, 2002) OR EXCLUDE (PUBYEAR, 1999) OR EXCLUDE (PUBYEAR, 1998) OR EXCLUDE (PUBYEAR, 1997) OR EXCLUDE (PUBYEAR, 1994)) AND (EXCLUDE (PUBYEAR, 1990) OR EXCLUDE (PUBYEAR, 1989)) AND (EXCLUDE (SUBJAREA, “AGRI”)) AND (EXCLUDE (LANGUAGE, “Chinese”) OR EXCLUDE (LANGUAGE, “Persian”))	36
Science Direct	A. public transport technology, public transport services, public transport and the environment, public transport management, public transport electric vehicles	13,627
	B. Between years 2018–2022	6701
	C. Topic, domain, access mode	359

shows the number of papers found in the WOS, Scopus, and ScienceDirect databases using the Keyword Plus tool, a keyword research tool designed and registered by the Keyword Plus company to search for information correlated with chosen keywords (public transport technology, public transport services, public transport and the environment, public transport management, public transport electric vehicle, and blockchain).

4.2.1. WOS Database

Results analysis: According to the research carried out in the WOS database, 60 documents were identified (most of which were published in 2020; see Figure 8). This highlights the important directions towards which researchers in the field of public transport have gone. This work highlights the orientation of the studies carried out and offers future research directions that are not or are poorly addressed so far, such as the use of blockchain technology applied to public transport and the transition to the intensive use of electric vehicles.

4.2.2. SCOPUS Database

We searched for the keywords public transport technology, public transport services, public transport and the environment, public transport management. The keyword “public transport electric vehicle” was excluded, because it was not found in research papers in the Scopus database.

Number of research papers: 116.

Selection criteria:

-

Between August 2018—2022—36 articles were identified;

-

English language—36 articles were identified (see in Table 5).

Analysis of research results: As shown in Figure 9a, 36 documents were identified and the majority of the papers were published in 2021. This highlights the focused directions by researchers in the field of public transport. This work highlights the orientation of the studies carried out and offers future research directions that were not or have been poorly addressed until now, such as the use of blockchain technology applied to public transport and to the intensive use of electric vehicles.

The trends of publications according to source, author, affiliation, and country are presented in Figure 9b.

4.2.3. ScienceDirect

Manuscripts from the ScienceDirect database were also utilized, following the same keywords that were used for Scopus and WOS databases. During the search process, 13,627 manuscripts were identified. The selection criteria used were the following:

-

Years: between 2018 and 2022—6701 manuscripts were identified (see Figure 10a);

-

Subject, domain, access mode—359 manuscripts (see Figure 10b).

Figure 10. (a) ScienceDirect—results by keywords and year; (b) ScienceDirect—results by keywords, year, subject areas, and access type.

Figure 10. (a) ScienceDirect—results by keywords and year; (b) ScienceDirect—results by keywords, year, subject areas, and access type.

All of these selection criteria led to 359 manuscripts in the research area.

4.3. VOS View Tools

VOSviewer is a software that develops scientific reports through bibliometric networks. The software is capable of developing bibliometric maps, including individual publications or journal research. The generated maps can be built on co-authorship, co-citation, bibliographic coupling, or citation relationships. Each item can be extracted and analyzed individually [67].

The general bibliometric maps for this analysis were obtained by following the steps further detailed. The first of them was to select the appropriate articles for our research and download the RIS extension in the VOSviewer program. Next, depending on the analysis that is being performed, the sequence underlined below was used:

VOS Viewer Tools (public AND transport AND blockchain) AND TITLE-ABS-KEY (public AND transport AND blockchain AND management) AND TITLE-ABS-KEY (public AND transport AND blockchain AND public transport and the environment blockchain AND public transport AND public transport technologists AND public transport electric vehicles AND public transport services AND public transport and the environment AND public transport management).

We had to choose the type of data and the map based on text data, and then we used RIS as the reference file manager and to represent the map by the full count method.

4.4. Journals Where Research Was Published

Figure 11 shows the visualization of all journals where the manuscripts were published in different colors.

The best-represented cluster is the red cluster. Some of the most common terms included in this cluster are “energy policy”, “sustainability”, “sensor”, and “journal of hydrogen”. The green cluster focuses on journals such as “transportation research”. The violet cluster has journals such as “renewable and sustainable energy” and “clean technology and environment”. The rose cluster refers to publications such as the “journal of the air and waste” and “atmospheric environment”. These results were used as main keywords.

Figure 12 presents the visualization of universities and research institutes with published works in this field of research, and the area in the center (marked in red) represents the locations with the most researchers.

Figure 13 shows the visualization of the authors’ collaborations in the analyzed fields.

Figure 14 shows the visualization of the countries where the research in the field was carried out by color codes.

5. Discussion

When applied to public transport, blockchain technology has several benefits and advantages, as follows [73,74,75,76]:

-

Every payment is secured;

-

Each person that performs this form of mobility will be able to view the number of tokens they possess and those used for different payments or contributions to the state;

-

Increased people’s confidence to carry out mobility with the means of transport provided by public transport in charge of the local public authority or the transport operator;

-

The possibility to increase the efficiency of the local traffic;

-

Reducing the use of private cars;

-

Reduction of greenhouse gases with the advantage of a consistent decrease in air gases level;

-

Reducing traffic accidents;

-

As for contributions regarding the public transport management, the major advantage is to promote public transport services.

By applying blockchain technology in public transport services, a series of benefits is obtained through a series of criteria, such as transparency, immutability, and distribution. In the beginning, the area presented a series of solutions to solve the problems that appear in this direction, which led to a series of changes in the current state of technology regarding public transport.

In [1], a review is made by analyzing papers that discussed the application of blockchain technology in the period of 2013–2020. The evolution of applications for this technology showed a growing interest in researching this field of interest. In conclusion, the paper considers that the blockchain is an alternative to databases in some cases and an inadequate input in other cases. Over time, it has been shown that this does not correspond to reality. Traditional databases are used in various scenarios.

The research in [2] is a review of the application of blockchain in the field of public transport, the Internet of Vehicles, with a survey aimed at the following directions: the use of blockchain technology with its opportunities and the evolution of technology over time, starting from classical encryption to the use of bitcoin with consensus protocols and smart contracts (Ethereum and Hyperledger). The strengths and weaknesses are identified by summarizing the work performed in existing research and future research directions.

A transparent and secured blockchain data storage network, which users can access with a key, is presented in papers [3,10,13].

In [4,14], the vulnerabilities to which the data are subjected by the application of blockchain technology are analyzed. The papers provide a summary of the vulnerabilities that are interpreted by the fact that no international standardization has been achieved.

In [5,8,9], mobility and transport in a smart city are analyzed, where a number of problems may occur, such as traffic congestion and environmental issues manifested as changes in air quality; the papers offer analysis of issues regarding sustainable mobility, transactions proposed by sharing mobility, and charging possibilities for electric cars and communication between vehicles, all of these being managed according to some criteria from which we try to obtain a series of ideas for future research.

The papers in [6,11,12] review the use of blockchain in transport applications and propose a methodology developed in several stages: presentation of the current research directions, problems encountered, and future directions for research. Their analysis shows that the technology approached is at the beginning of the road and further research must be carried out to reach an optimal level of application. Additionally, as a conclusion, it is expected that this technology will contribute to increasing the quality of life.

In [7], there is a review of the application of blockchain in different areas. The aim of this study was to manage the use and benefits of this technology in different key areas, such as supply chain stores, medicine, and managing the privacy of personal data. A number of inappropriate problems in various production sectors are highlighted. These reported issues will act as future research directions.

The summary of the results from [1,2,3,4,5,6,7,8,9,10,11,12,13,14] can be found in

Table 6. Summary of review results for future research.

Revision Type	Application Concept	Practical Results	Reference
Blockchain evolution	Database	General summary	[1]
Using blockchain technology	Sounding	Transport summary	[2]
Data storage	User access	Key user access summary	[3]
Blockchain vulnerabilities	x	x	[4]
Mobility and smart transportation—smart city	Suggest a platform	Suggestions for future research	[5]
Revision in transport	x	x	[6]
Using blockchain technology	x	Results for future research	[7]
Revision in transport	x	x	[8]
Revision in transport	x	x	[9]
Data storage	x	x	[10]
Revision in transport	x	x	[11]
Revision in transport	x	x	[12]
Data storage	x	x	[13]
Blockchain vulnerabilities	x	x	[14]

Note: x—it is not presented.

:

Regarding future directions, we can talk about the implementation of new technologies to solve the problems that have been identified in the development and transformation of localities into smart cities.

The review was conducted in the five directions of the public transport (public transport technology, public transport services, public transport environmental, public transport management, public transport electric vehicle) where blockchain technology is used, which supports the mobility process and can be improved. Although this technology is in its infancy, it promises many benefits.

This paper offers a wide range of solutions that have been identified in existing research that can be applied by local authorities, in particular to more effectively manage the situation in the locality in terms of public transport and, last but not least, by researchers.

6. Conclusions

This paper presents the current status of public transport services that provide directions for beginning researchers. The advantage of this research lies in the method used—the PRISMA method for carrying out analysis in specialized literature.

The analysis focused on research published in the last two years and the conclusions of this study are summarized in tables according to the research direction targeted, as follows: economic, environmental, social, and public awareness proposals.

Thus, the main contributions of this study are as follows:

-

A classification of the research carried out on the transport of persons, taking into account several criteria for main subsystems of the public transport system;

-

Based on the critical analysis performed, the main features of a new public transport platform based on blockchain technology are identified;

-

The results presented can help interested researchers to identify ways to encourage people to use public transport, giving up personal cars, and to ensure their confidence in data privacy and passenger safety.

Unlike the solutions proposed in the existing literature, a blockchain-based solution must take into account car traffic, which depends on actors such as the local public administration, the public transport management system, transport operators, and users as the participants in local public transport. All of these entities contribute to uploading data, updating databases, and querying them. Thus, if electric buses are used mainly, there will be benefits for both the transport operators and the users, as well as for the environment.

Although the blockchain allows decentralized and secure means of authorizing transactions and eliminating the need for a centralized authority, it is necessary for the public authorities to adopt some regulations that can encourage passengers’ interest in using public transport.

The advantage of this study are for researchers who are trying to find ways to convince both local authorities and people who use a means of transport to achieve mobility. As part of the suggested methods, the use of distributed databases that are applied in practice will be able to contribute to the transformation of localities into areas with a degraded environment in terms of CO₂ concentration.

The method used in the review of the existing literature and the technique used in public transport may be useful for the development of future research. This study proposes the use of a new technology such as blockchain in public transport. Thus, a new directive for the transformation and improvement of public passenger transport is facilitated.

The systematic analysis performed in this study provides researchers with a current perspective of the challenges in public transportation correlated with passenger choices and environmental implications. Another aspect of the novelty in this field is the proposal to use blockchain technology, which will lead to new solutions for the problems and challenges that have arisen in recent years. The method used for the review is a universal one, but what must be remembered is the fact that the proposed blockchain technology is a new one, which leads to a new conceptual framework being developed. A limitation of the study would consist in the fact that it is not fully tested in practice, the authors having as an immediate goal its implementation. The study is based on the results from the published literature and the research can be extended using future publications in the field of public transport, following the same steps: identifying papers, verifying the qualitative results, and carrying out simulations and tests for different cases.

A comprehensive analysis of the current state of public transport was carried out, the orientation being directed towards the application of blockchain technology to highlight the results obtained in public transport correlated with economic and environmental influences. Thus, the problems and solutions proposed in the research were identified in relation to the topic addressed, namely public transport and the use of blockchain technology. The evaluation followed the frequency with which the publication was made over time, the area in which it was published, the domain, and the language of publication. The list of evaluations in the field of transport is large, but the following directions were extracted: public transport technology (PTT), public transport services (PTS), public transport environmental (PTE), public transport management (PTM), and public transport electric vehicles (EVs). Blockchain technology in these directions is less well represented or not at all. A greater coverage was recorded for public transport technology and public transport services (PTS) if we refer to searches in databases such as ScienceDirect, to which is added public transport management in Scopus and WOS. Few studies proposed the use of blockchain technology.

As for places of publication, most of the examined papers appeared in renowned journals and conferences, which highlights the fact that the studies have a high scientific degree. As for the number of studies, there has been an increase in them in the last three years.

From the point of view of the strategies encountered, they are diversified and led to a high reliability of the systematic study. In order to make a decision, database searches and manual searches were carried out.

In order to guarantee the use of shared public transport, instead of transport by personal vehicles, it will be necessary to ensure high standards in terms of quality. Such factors are: spatial accessibility, time slots and frequency of service, punctuality and reliability, competitiveness in terms of travel time, the existence of direct connections or adequate transfers, and the comfort and safety of the means of transport.

The efficiency of public transport is observed in its integration (refers to easy mobility) from a spatial, organizational and tariff point of view.

Blockchain technology can be successfully used in public transport-oriented applications. This paper aimed to provide an overview of the existing literature regarding the use of these technologies in public transport. At the same time, it provides information on the future directions of research, for those who approach research in the field of using blockchain technology in public transport. The bibliometric analysis was carried out according to keywords in articles and academic journals from the period of 2018–August 2022. The research carried out identified the most important studies in the field addressed, highlighting the benefits of sustainable transport by reducing consumption and carbon emissions, increasing the number of electric cars and ensuring an adequate level of energy security and independence.

This study identified research directions for sustainable transport development that relate to low- and zero-emission, energy-efficient, and affordable transport solutions, including electric vehicles.