1 Introduction

The fully automatic operation (FAO) system is a new generation of train control system in urban rail transit that automates the whole process of train operation based on advanced technologies such as modern computer, communication, control and system integration [1]. The FAO system is of great significance for further improving the safety and efficiency of urban rail transit, reducing operational costs, and improving the automation and intelligence level of the equipment. As shown in Fig. 1, the International Union of Public Transport defines the grade of automation (GoA) of train operation into four grades [2]. Both the GoA3 and GoA4 are collectively referred to as FAO. The difference is that there are crew attendants on trains to monitor the closing of train doors and handle interference events with GoA3. Trains running with GoA4 do not require on-board crew attendants, which is highly autonomous and unmanned. When a fault or failure occurs, the ground personnel will be sent to the train to deal with it [3]. The FAO system has the following advantages compared to the Communication Based Train Control (CBTC) system. From the technical aspect, the FAO technology improves the automation level of the urban rail transit system, which reduces the labor intensity of operators and human errors. Moreover, the FAO technology increases the uniformity of train driving control, contributing to a better energy-saving effect. In addition, from the perspective of rail transit industry, the construction of FAO system promotes the development of rail transit infrastructure, which brings significant social benefits.

Figure 1
figure 1

GoA of urban rail transit [1]

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This paper summarizes the whole process of the architecture design, construction and management of the FAO system, which can promote the standardization of the domestic FAO system in China and play a guiding role in generalizing the construction of the domestic FAO system in different cities. The main contribution of this paper includes the following three aspects.

  • The architecture and characteristics of the FAO system are introduced, and the analysis method of system design requirements is described based on the human factors engineering.

  • The critical technologies of the FAO system are introduced in the view of signaling system, vehicle system, communication system, traffic integrated automation system and reliability, availability, maintainability, and safety (RAMS) assurance.

  • Based on the independent practical experience of the FAO system, this paper summarizes the management methods for the construction and operation of FAO lines and prospects its future development trends based on the advanced technologies such as artificial intelligence, big data and cloud computing.

2 Worldwide history of FAO system

Owing to the advantages of the FAO system and the innovative technological upgrade, many countries all over the world are accelerating the research of FAO system. The worldwide development of FAO system is concluded into three stages: exploration, promotion, and mature application.

2.1 Exploration stage

During the experimental and exploratory stage, the train-to-ground communication adopted the inductive loop non-continuous communication and the fixed block technology was used to separate the train. The opening and closing of the door, the train starting and entering the station were still operated by drivers, which did not reach the GoA4. The automatic operation system in this stage was mainly used in special lines with small passenger flow such as park sightseeing lines and airport ferry lines. For example, in 1959, the United States officially launched the study of driverless train operation of the Times Square-Central Railway Station Ferry Line in New York. The test experiments were conducted in 1960, and the trial operation was carried out in 1961. Later, the technology was put into practice without crew attendants in 1962. The fixed block technology was used and the train speed was limited to the range from 27 km/h to 40 km/h. This line was recognized as the first fully automatic urban rail passenger line in the world [4]. In 1965, Westinghouse Electric Corporation proposed to construct unmanned, high-frequency service, and economically viable public transportation system, which was named as SkyBus in the South Park near Pittsburgh [5]. Since 1964, London has conducted verification experiments for the mixed operation of automatic operation and manned driving trains. The Victoria Line, the first FAO line in London, was put into service in 1968 [6, 7]. In 1975, West Virginia University in the United States opened an FAO line called Morgantown PRT which is still in normal operation now [3].

2.2 Promotion stage

In February 1981, the Kobe Island Line that applied the automatic guided transit (AGT) system was open in Japan. This line realized the whole process automation of main line operation and was considered as the first light rail line with GoA4 in the world [7]. On April 25, 1983, the Lille 1 line in France used platform screen doors to isolate passengers from the track for the first time to ensure passenger safety and reduce the probability of track intrusion in the platform area. In 1985, the Canadian Expo overhead line adopted the advanced rapid transit (ART) system, which was the first application of the moving block technology and CBTC system in urban rail transit [7]. Besides, the Paris Line 14 opened in 1998 was the first FAO line in Paris. The automatic train operation system designed by Siemens can adjust the speed and density of trains according to the needs of operation and dispatching. In addition, the Northeast Line of Singapore opened in June 2003 was the first FAO line with large-capacity and the operation range of the FAO system covered both the main line and depot. The signaling system of this line was developed by Alstom. The maximum train speed was 90 km/h and the minimum headway was two minutes during peak hours. In June 2008, the U3 Line of Nuremberg was the first FAO line that was put into operation in Germany. A relatively complete system of regulations and industry standards were formed, including emergency, communication, and fire protection standards [5]. Besides, the Red Line of Dubai Metro in the United Arab Emirates opened in 2009 was the longest FAO line in the world, with a total length of 52.1 km. In the Red Line, the signaling system was provided by Thales. The minimum headway was 90 s and the maximum train speed was 90 km/h [3].

In the promotion stage, the FAO system has been applied to mass transit systems. Notably, the new technologies emerged, including moving block, CBTC system and platform screen doors, which laid a solid foundation for the mature application of FAO system.

2.3 Mature application stage

In order to establish an integrated and innovative European railway market and enhance the competitiveness of railway, the European Union (EU) organized relevant industry associations, equipment manufacturers and operators to initiate a series of research projects from 2004 to 2012. Among them, the goal of the technical research project MODURBAN was to design and develop a next-generation urban rail transit system with open system structure and interfaces. The project completed various application tests of the entire urban rail transit system in 2009 (marked by the Madrid Metro test in December 2008), and formed a series of specifications (functional requirements specifications and technical specifications) that were suitable for all operators and covered the manual driving and FAO [8]. The research results of this project were adopted by the International Electrotechnical Commission (IEC) and the European Committee for Electrotechnical Standardization (CENELEC), which was an important sign of the mature application of the FAO system.

During this stage, the FAO system has been gradually applied to lines with large passenger demand and high frequency service, which can realize automatic operation in the whole area (including parking lots or depots). The typical representative was the Paris Line 1 in France which was completed in 1900. This line was about 16.4 km and included 25 stations, and was regarded as the busiest and most crowded line in Paris. In 2007, the Paris Line 1 began to be renovated. After overcoming many technical challenges, it was put into fully automatic operation in April 2013 and became the first metro line that was transformed from manual driving to fully automatic operation in the world [3].

Meanwhile, the promulgation of relevant international standards (such as IEC62290 and IEC62267) also showed that the FAO technology had gradually matured from theory to practice.

2.4 The development of FAO system in China

Before 2000, the urban rail transit in China was not well developed. The total length, density and passenger transport proportion of rail transit was far below the average level in the world. After 2000, urban rail transit in China developed rapidly. By the end of 2021, 51 cities in mainland China had opened urban rail transit, with the total mileage of about 9000 km. With the density of the line network and the increase of passenger flow, higher requirements are put forward for both the construction and operation of urban rail transit. It is necessary and urgent to study and develop independent FAO technology.

The Beijing Capital Airport Express (BCAE) opened in July 2008 was the first FAO line in China, but the technology was introduced from France [3]. In April 2010, the Shanghai Line 10 began to operate with the driverless fully automatic system. Both the BCAE and Shanghai Line 10 used the FAO technology provided by Alstom. In November 2010, the APM line of Zhujiang New Town in Guangzhou adopted the CITYFLO 650 system provided by Bombardier and was put into operation with GoA4. Besides, the South Island Line in Hong Kong was open with GoA4 on December 28, 2016. Especially, the fully independent equipment and FAO technology were applied in the Beijing Yanfang Line at the end of 2017 which was in GoA3 [9] and began to operate with GoA4 in 2020. At present, 12 cities in China are constructing or planning FAO lines, with a mileage of 1150 km [3]. In the future, Lines 3, 12, 17, 19 and the New Airport Line in Beijing and Lines 14, 15, 18 in Shanghai will adopt the FAO system and be constructed with GoA4. In addition, Shenzhen, Hangzhou, Chengdu, Nanjing, and Nanning are also carrying out relevant planning and design activities, which show that the application of FAO technology has become the mainstream trend in the future.

3 Analysis of design requirement

3.1 Architecture and characteristics of FAO system

Based on the driverless function and oriented to improve the safety and efficiency of the whole system, the FAO system realizes the coordination of relevant systems and man-machine cooperation to ensure the safety and efficiency of the whole train operation process. The FAO system is a complex system composed of 7 major disciplines, 31 subsystems and hundreds of thousands of collection points. As shown in Fig. 2, the system architecture is divided into three levels, i.e., the central level, the station level, and the on-board level. The functions of the three levels are described as follows. The central level is to monitor train operation and serving passengers and the station level is to monitor and control the equipment in the station. The on-board system is to implement the train control according to the command from the central and station level [9].

Figure 2
figure 2

Architecture of FAO system [1]

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Compared with the traditional system, the FAO system has the following characteristics and intension.

(1) Safety of the whole system. In the design of FAO system, the protected objects for safety include both the train operation and the passengers inside and getting on/off the train. Besides, special consideration should be taken to make up for the safety requirements when the driver is not on board. Therefore, the FAO system focuses on the passenger safety, which reflects the concept of passenger-oriented service.

(2) Automation of the whole disciplines. The FAO system is designed in accordance with the unattended train operation (UTO) mode. The availability of FAO system must be high enough to ensure the safe train operation in the case of the absence of drivers. Generally, the functions and performance of the equipment (such as vehicle and signaling system) should meet the requirements in UTO mode.

(3) Automatic operation of the whole area, whole process and whole period. The functions of the FAO system cover the whole areas including but not limited to depot, test line, transfer track, main line section, station, storage line and turn-back line. The whole process of train operation includes wake-up, self-check, operation on the main line, turn-back, and returning to the depot. Moreover, the automatic train operation ranges from the beginning of operation in the morning to the end of operation in the evening.

3.2 Requirement analysis of system design based on human factor engineering

The train control system is a human-machine hybrid system. As the last safeguard line in the automation system, human still plays a vital role in the safe and reliable operation of urban rail transit. If the human-machine relationship does not match in the design, development and application of the FAO system, there may be problems such as automatic complacency, automatic satire, personnel skill degradation and lack of situational awareness [10]. FAO has brought about innovative improvement in the rail transit system, which is essentially the redistribution of human-machine functions related to train operation. In addition to the design of system equipment, operational rules and emergency response strategies should be developed. Hence, the human factor engineering theory is introduced to analyze the design requirements of FAO system and study the interaction between human and machine. In this way, the design and evaluation of system products can be improved, which contribute to the enhancement of system performance, system safety, and personnel satisfaction.

According to the human-machine interactive characteristics in FAO system, an interactive operational model for the personnel in key positions is constructed. Using the method of core task analysis (CTA), the core tasks in FAO are analyzed based on the operational scenarios. Further, the requirement analysis of train control system is carried out in terms of technical reliability, personnel skills, rules formulation and passenger requirements. The overall flow of the method is shown in Fig. 3.

Figure 3
figure 3

System design requirements analysis framework based on human factor engineering

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The FAO system covers several operational scenarios at different grades of automation, and each scenario contains a set of interrelated tasks. The fully automatic operational scenarios are decoupled and divided into the operation scenarios and operational rules. According to the main line of daily train operation, the 41 scenarios are formed, which includes 18 normal scenarios and 23 abnormal scenarios (see Fig. 4). Operational rules, making the overall formulation of the operational organization work and covering all scenarios in operation, are the top-level documents of the entire operational organization structure and regulation text system. The contents of the operational rules mainly include the position setting principles, the overall position responsibilities, basic functional requirements of each scenario, work contents, processing flow and personnel interaction.

Figure 4
figure 4

Fully automatic operation scenarios

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Generally, the requirement analysis of FAO system design mainly involves the following three aspects.

(1) Formulation of the operational model. During the process of train operation, the onboard personnel obtain the scenario information of the internal and external environment through their own visual, auditory, and tactile sense channels, receive the command information from the dispatcher in the control center, and provide service and response information for passengers. In combination with the objectives and constraints of the current scenario, the perceived information is cognitively processed and stored in short-term working memory. Moreover, rules and knowledge corresponding to the perceived information in long-term working memory are found from long-term memory to make decisions and execute corresponding actions. Based on the information processing model of attention resource allocation, the operational model for the train control system is proposed to replace the onboard personnel.

(2) Core task analysis based on operational scenarios. In order to clarify the design requirements of the FAO system, the train driving tasks are firstly analyzed from the driver’s point of view. It is obtained that four main tasks for FAO system are to drive the train on the track, stop at the station, care for passengers, and interact with other roles. Based on the environment and objectives under different scenarios, the basic operational functions of the train are clarified. Further, the operation tasks are confirmed by combining the GoA of the current FAO system, and task analysis is conducted based on the CTA method, which identifies the core tasks of specific work and obtains result-oriented work contents.

(3) Requirement analysis of the train control system. Combining the operational model and results of core task analysis, it can be found that the tasks of FAO system still cannot be executed without the participation of personnel. In order to reduce human intervention to achieve the UTO mode, the existing automation problems of the current train operation system are analyzed from four aspects, i.e., technology, personnel, regulations, and passenger requirements. Corresponding solutions are proposed, such as further improving the reliability and technical availability of equipment, clarifying the technical needs for personnel and strengthening the skill training and assessment for existing personnel, formulating scientific and reasonable cooperation rules, and enhancing the public’s correct understanding of the FAO system.

4 Key technologies of FAO system

The FAO system is the highest level of urban rail transit automation, and the key technologies involve the signaling, communication, vehicle, traffic integrated automation, and RAMS assurance.

4.1 Key technologies of signaling system

The signaling system is regarded as the “nerve and brain” of the FAO system, and it plays a vital role in ensuring the safe and efficient operation of the FAO system [11]. In order to realize the automatic train operation in the whole area, whole process and whole period, the following key technologies are applied to the signaling system.

(1) Automatic sleeping and wake-up system. Figure 5 shows the structure of the automatic sleeping and wake-up system in the FAO trains. The overall process of the sleeping and wake-up includes: the automatic train supervision (ATS) system in the control center sends a sleeping/wake-up command automatically to the train at a predetermined time point according to the timetable. The sleeping/wake-up command is sent from the wireless access point (AP) equipment of the control center backbone network through the wireless communication network, and the on-board AP equipment sends the command to the wake-up unit through the local network. Then the control command is sent to the on-board equipment by the wake-up unit to power on/off the equipment to realize the sleeping/wake up of the whole train. The basic flow of the wake-up process is illustrated in Fig. 6. The wake-up and AP equipment are powered by on-board batteries, and head-to-tail redundancy settings are adopted to ensure the working status and availability of the system during the whole period.

Figure 5
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Structure of automatic sleeping and wake-up system for fully automatic trains

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Figure 6
figure 6

Basic flow of the wake-up process

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(2) Continuous positioning in the whole process of train operation. For ensuring the safety protection in the whole area of the FAO system, the train should have effective and precise positioning function after being awakened in the depot. To realize the initial wake-up positioning of the train, wake-up balises are arranged at both ends of the train stopping position in the sleep/wake-up area. In this way, the locations of the head and rear of the train can be received immediately when the train is woken up. And the train position and running direction are obtained. Specifically, the running direction of the train is the connection direction of two continuous balises. The head location \(L_{\text{h}}\) and rear location \(L_{\text{r}}\) of the train can be calculated by the equation (1), where \(x_{\text{b}}\) is the location of the second balise; \(x_{\text{r}}\) is the displacement of the train after receiving the signal of second balise; \(D_{\text{bh}}\) is the distance from the balise antenna to the train head, and \(l_{\text{b}}\) is the radiation range of the balise antenna; \(L_{\text{t}}\) denotes the train length. During the train operation process, the multi-sensor fusion positioning technology is used to calculate the periodic displacement according to the train speed, continuously updating the train position. Further, the train position is corrected based on the information of the absolute position correction equipment laid on the fixed positions, e.g., balise on the line

$$ \textstyle\begin{cases} L_{\text{h}}=x_{\text{b}}+ x_{\text{r}}+D_{\text{bh}}+l_{\text{b}}, \\ L_{\text{r}}=L_{\text{h}}- L_{\text{t}}. \end{cases} $$
(1)

(3) High-precision train stopping control. The stopping control technology applied in the FAO system not only realizes the high-precision train stopping at the stop point, but also adjusts and corrects the stop position automatically under abnormal conditions caused by environmental factors to ensure the safety of passengers. When the train stops abnormally, the skip-stop function is used to automatically adjust the train stopping position. During the skip process, the automatic train operation (ATO) system outputs the skip command and traction force, while the automatic train protection (ATP) system protects the skip process to improve the availability of the skip benchmarking.

(4) Safety control of the train door and platform screen door. The train door and platform screen door are the channels connecting the two passenger spaces of the movable train and the platform, which are the key parts of the system protection. In the FAO system, the detection equipment is installed between the train door and platform screen door to determine whether there is an obstacle between them by the principle of geometric optics. In addition, the accurate fault identification and linkage control technology of train door and platform screen door links the on-board signaling system, interlocking system, train control and management system (TCMS) and platform screen door system to automatically realize the integrated treatment of the train door and platform screen door faults, which can protect the safety of boarding and alighting passengers and realize the efficient stopping operation.

(5) High-efficiency driverless turn-back. The FAO system can realize the automatic turn-back, including automatically running into the turn-back area, switching the train-end, and entering the next transportation operation section with no unmanned driving. The turn-back capability is the bottleneck restricting the improvement of line transportation capacity, which is mainly reflected by the minimum train headway between preceding and following trains. By further optimizing the process of turn-back operation, the processing delay of the train turn-out route is greatly reduced and the more precise control of line resources is realized, thereby improving the turn-back capability of the line.

(6) Systematic energy-efficient control. On the basis of meeting operational requirements, passenger comfort and convenience, the optimization theory, multi-objective control algorithms, and collaborative control theory are applied to optimize the train driving strategy and timetable such that a comprehensive energy-efficient operation strategy can be achieved. The traction energy consumption is efficiently reduced and the regenerative energy is fully reused [12]. Meanwhile, taking passenger service as the core, the station equipment is controlled based on the timetable information through multi-disciplinary linkage to realize the automatic opening of stations and the activation of the electromechanical equipment, contributing to the system-level energy saving.

4.2 Key technologies of vehicles

The vehicles are the carriers of the FAO system and play the role of the executor. To realize the overall control and management with the multiple systems such as signaling, traffic integrated automation, communication, and platform screen doors, and to ensure safe and reliable automatic operation, the key developed vehicles technologies include the following aspects.

(1) Design of closed console for FAO vehicles. The console of FAO vehicles is developed with considering the compatibility of the FAO and manual driving modes. With the innovative design methods, the fully-enclosed console structure is developed to realize a smooth transition from manual driving to FAO. Further, the 3D software CATIA is used to establish the model to ensure the applicability and reliability and the carbon fiber material is used to realize the integration of the cab and the console.

(2) Implementation of fully automatic control function. The fully automatic control function of the vehicles in the FAO system mainly depends on the TCMS. In the FAO system, the function of controlling the remote train automatic wake-up and sleep has been added to TCMS. If an important circuit breaker trips or other abnormal conditions occur during the train operation, the TCMS automatically monitors the state of the circuit breaker and realizes the remote reset control function. When the passenger triggers the emergency alarm button, the TCMS plays the role of a bridge between the vehicle and the control center to ensure that the passenger request is quickly responded [13].

(3) Vehicle derailment and obstacle detection. The obstacle and derailment detection equipment are newly equipped on the FAO vehicles to realize the automatic identification of the foreign object on the line and ensure the safety of vehicles and person entering the line accidentally. Moreover, this system has an automatic linkage function with the control center and other systems on the vehicle. In case of emergency, it can automatically trigger the emergency braking, report the situation to the control center, and automatically resume the operation after confirming that the emergency is eliminated through communication with the operation and maintenance personnel [14].

(4) Fully automatic status monitoring and fault warning. The subsystems equipped on the FAO trains mainly are the traction, braking, auxiliary, door control, air-conditioning, storage batteries, pantograph-catenary, running gear detection, and on-board signaling system. The vehicle equipment status information and on-board automatic train control (ATC) information collected by the TCMS system are sent to the intelligent vehicle maintenance server through the vehicle-ground Wi-Fi channel and Long-Term Evolution for Metro (LTE-M) respectively to realize the remote centralized monitoring of the vehicle status. Furthermore, the intelligent vehicle maintenance server carries out the generalized classification of various types of vehicle faults, establishment of knowledge graph and in-depth analysis of correlation causality, which can effectively decompose and identify the correlation between different faults and accurately obtain the causes and scopes of faults. Besides, based on the large amount of historical on-board data, the algorithm model of fault warning can be formulated by the fusion algorithm of self-learning and fault mechanism analysis to realize the accurate warning of vehicle faults and reduce the fault probability of the vehicles in operation [15]. Thus, the operational safety is guaranteed.

(5) Emergency handling. In response to the need for rapid and automatic emergency handling under the driverless condition, the remote-control technology for key systems of FAO trains has been developed to realize the remote bogie brake removal, remote reset and restart, remote reclosing, remote control of the flow receiving equipment, and remote braking application and release functions. In addition, the on-board Passenger Information System (PIS), Public Address (PA), and Closed-Circuit Television (CCTV) systems are linked under the emergency situations, so that the control center can monitor the emergency area of the vehicle, and the direct intercom function between passengers and the control center can be activated. At the same time, the on-board PA system automatically broadcasts the emergency situations to stations, trains, and sections, which helps the station staff in evacuating passengers and guiding the passenger flow such that the risk of secondary disasters from accidents is minimized [16, 17].

4.3 Key technologies of communication system

In the FAO system, the LTE-M system is mainly used for the transmission of vehicle-ground information. The transmitted data mainly includes train control information, train emergency text, train running status, PIS information, video monitoring information and trunked dispatching service, which realizes the integrated carrying of multiple services. In the FAO system, the LTE-M system applied mainly adopts the following key technologies.

(1) Multi-service priority guarantee technology. The various services carried by the LTE-M system have different effects on the stable operation of the FAO system. In order to prioritize the quality of the key service, it is necessary to differentiate the end-to-end service quality. The LTE-M system designs a nine-level quality of service (QoS) guarantee mechanism to reasonably allocate resources for different services according to their service priorities. In this way, the requirements of delay, packet loss rate and transmission speed of different services can be met under various scenarios such as admission and congestion. In the FAO system, the end-to-end unidirectional transmission delay of the service data is less than 100 ms, the theoretical plane delay of the switching data is less than 80 ms, and the multiple retransmission mechanism ensures that the packet loss rate is much lower than 0.5%. The length of switching zone between two successive base stations \(L_{\text{sz}}\) can be obtained by the equation (2), where \(D_{\text{rsrp}}\) is the difference of the reference signal receiving power between two successive base stations; \(L_{\text{dz}}\) denotes the length of the delay zone; \(T_{\text{m}}\) is the measurement duration; \(T_{\text{sw}}\) is the switch delay; \(v_{\text{t}}\) represents the train speed

$$ L_{\text{sz}}=D_{\text{rsrp}}/L_{\text{dz}}+2*(T_{\text{m}}+T_{\text{sw}})*v_{ \text{t}}. $$
(2)

(2) Co-channel interference suppression technology. In order to ensure the orthogonality between the channels of different cells in the same-frequency networking mode, the Inter-Cell Interference Coordination (ICIC) technology is adopted in the LTE-M system of the FAO system to solve the co-channel interference problem. The ICIC technology considers the resource usage and load in multiple cells. By managing the radio resources, the resource blocks of neighboring cells are separated or the transmission power on the used resource blocks is decreased to avoid resource collision, which suppresses the Co-channel interference between neighboring cells.

(3) High availability technology. The high availability technology of the LTE-M system consists of the core network and train access unit (TAU). Through shielding possible faults and hot standby redundancy, the high availability technology of the core network achieves seamless switching and dual-net redundancy networking. Further, the solutions to improve operational availability are respectively developed from the three levels, i.e., software design, hardware platform design and networking design [18]. Besides, the redundancy and switching mechanism of the on-board TAU equipment in the FAO system improves the availability of the vehicle-ground wireless communication system.

4.4 Traffic integrated automation

The FAO system adopts the integrated automation architecture to deeply integrate the signaling system and integrated supervisory control system, which realizes the integrated automation system and breaks the information barrier between various specialties and realizes the professional linkage monitoring based on data sharing. The traffic integrated automation system (TIAS) realizes the real-time monitoring of trains and the remote service of passengers by the control center to improve the intelligent control ability of the whole process. The key technologies in the TIAS are described as follows.

(1) Multi-disciplinary collaborative control technology. The innovative design of ‘double buffer’ and the transposition transmission communication fusion technology are adopted to realize multi-disciplinary and large-capacity heterogeneous real-time data processing, and real-time display and rendering of large-scale data. The dispatching linkage buses for the traffic control, power, environment, passengers, vehicles, and maintenance are unified to realize the man-machine collaborative intelligent monitoring based on the time and event sequences, which can meet the requirements of the FAO system and further improve the dispatching efficiency. Besides, the monitoring and control, emergency disposal and remote service for all electro-mechanical equipment on the trackside, service trains and passengers in the train are realized by the control center, which further improves the operational safety and passenger riding experience in the FAO mode.

(2) Multi-disciplinary linkage technology in emergency. Through the design of a new distributed real-time data engine that supports the object-oriented modeling, the intelligent management and control of the whole train operation process and the intelligent coordinated joint control between complex systems are realized. The emergency response linkage control functions, including the alignment isolation, creep mode, emergency call, vehicle smoke alarm linkage and detection of hurting people between platform doors and vehicle doors, are innovatively enhanced. Compared with the traditional emergency handling, the linkage controlled capacity is increased by more than 20% and the emergency response time is reduced by about 30%, which can further improve the intelligent processing capability under the disaster and fault mode and enhance the operation safety of the urban rail transit system.

(3) Multi-disciplinary intelligent maintenance technology. By using the heterogeneous data cleaning, data fusion and diagnosis fusion technology, the diagnosis data of the multi-disciplinary equipment are transmitted and reconstructed to reduce the false alarm rate of the equipment. Moreover, the immediate and comprehensive decision-making alarm system based on the samples is developed to detect the on-line state and predictively diagnose the core electromechanical equipment. A set of standard enterprise soft bus (ESB) technology based on Extract-Transform-Load (ETL) is utilized to realize seamless and closed-loop control for the maintenance management system and online monitoring system, which can fulfill the refined management and reduce the equipment maintenance cost as well.

4.5 Life-cycle RAMS assurance

In order to ensure the highly safe and stable operation of the FAO system, and to realize the automatic train operation in the whole process and different whether condition, the FAO system is planned and designed according to the advanced international railway safety standards, i.e., RAMS design method. The indexes are allocated to each specialty, subsystem, and equipment. In the life cycle of requirement analysis, design, manufacturing, installation and commissioning, the safety assessment and RAMS management of the whole process are achieved (see Fig. 7).

Figure 7
figure 7

RAMS management activities in different stages of the life cycle

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(1) Life-cycle RAMS engineering design. By introducing the methods of top-level design, layer-by-layer allocation and failure mode analysis, a consistent technical specification of RAMS indexes is proposed from the perspectives of the top-level system and each subsystem. Using the robust design method and the analysis method of potential failure mode, the RAMS indexes are adapted to the design scheme in the overall system design stage to ensure that the RAMS indexes are fully considered in the detailed design process. Besides, the guideword-based hazard mode identification technology (GHMIT) is developed to analyze the safety of multi-disciplinary and comprehensive scenarios. In addition, the implementation technology of RAMS is optimized, and the product integrated development platform is constructed to support the research and development of the life-cycle products, which can provide technical and tool support for the engineering design of the FAO system.

(2) Differential-mode diversified redundancy mechanism. In the dispatching layer, the multi-role remote multiple redundancy design is implemented. The system is equipped with the main and standby control centers, and the two centers are respectively set with hot and standby redundant servers, which realizes the quadruple redundancy of the central-level server. Traffic dispatching, power dispatching, environment dispatching, vehicle dispatching and passenger dispatching can switch the control function through authority management, which enhances the redundant control of the FAO system. The reliability and availability of the FAO system can be improved through the redundancies of the key components of vehicles, vehicle-ground wireless communication, and head-tail sensors (speed measuring equipment, Balise Transmission Module (BTM), etc.) [9].

(3) Verification and validation of the whole process. The whole process verification and validation system is constructed in terms of the indoor test, template segment joint commissioning and trial operation. Specifically, the multi-level simulation test environment and dynamic configurable FAO semi-physical simulation test platform are built, and a number of test cases are used to ensure the complete test of the products and system. Moreover, the functional integrity and stability of the FAO system are fully verified via the joint commissioning and test in the template segment to achieve the project expectations. Further, the system function, performance and service level are verified through the trial operation stage with the intervention of the operation department and passengers.

5 Construction and operation management of FAO system

The FAO system is a new developing trend of urban rail transit technology. In the new round of large-scale construction of urban rail transit, it is urgent to vigorously develop and apply the independent FAO technology and equipment. To meet the needs of high-level construction of FAO system and provide safer, faster, more punctual and comfortable operational service, it is necessary to establish a set of effective new modes for construction and operational management.

5.1 Construction management of FAO system

5.1.1 Characteristics of the FAO construction management

To establish the construction management mode of FAO system, the characteristics of constructing FAO system are firstly analyzed as follows.

(1) The complex top-level requirement of FAO system. In the FAO system, the driver’s traditional work will be redistributed to equipment, station staff and dispatcher. Different top-level requirements of specific projects will lead to different function allocation, which results in different scenarios, operational rules, equipment functions and equipment configurations.

(2) The complex multi-disciplinary interface of FAO system. The FAO system involves multiple disciplines, such as vehicle, signaling, integrated supervision and control, communication, platform door, vehicle base and so on. The interfaces between the disciplines are more complex and closely connected.

(3) The high safety requirements of FAO system. The degrees of intelligence, automation and complexity of the FAO line are higher than those of the traditional lines, and higher requirements are put forward for the safety and reliability of the system.

5.1.2 Construction management process of FAO system

As shown in Fig. 8, compared with the traditional lines, the construction management process of FAO system has new and developed construction steps. Concretely, before the preliminary design, the technical system architecture of the FAO system is established based on a series of documents such as the top-level requirement analysis, operation scenarios and so on to clarify the top-level operation requirements, construction standards, new functions, new equipment, functional allocation of various specialties and key technical schemes. Besides, the indoor-integrated test is added between the design liaison and integrated joint commissioning. Additionally, the joint scenario discussion and determination of the core system integration scheme are added in the contract negotiation. The work of deepening the operation scenario is added in the design liaison, and the template segment joint commissioning is added to the integrated joint commissioning. Further, the stability test is added in the trial operation stage. Here, the corresponding construction management methods are respectively summarized for the construction characteristics in Sect. 5.1.1.

Figure 8
figure 8

Construction management process of FAO system

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(1) Operational scenario management for Characteristic 1. The key points are to clarify the top-level requirements and to build the technical system with the operation scenarios and operational rules as the main parts. Generally, the technical system of the FAO system can be composed of the top-level requirements analysis, operation scenarios, operational rules, as well as key technical solutions and interface scheme of the core system.

(2) Integrated joint commissioning management for Characteristic 2. The indoor and outdoor engineering conditions are fully utilized in the process of construction management. According to the outline of joint commissioning and test of the FAO system, the four-stage joint commissioning and test work (including the parking joint commissioning, template segment test, whole-line joint commissioning and timetable running test) are carried out to ensure full commissioning of the FAO system.

(3) RAMS management for Characteristic 3. The safety requirements are put forward from the perspectives of the whole system and each subsystem. In the life cycle, the hazard analysis technology is used for the RAMS management of the whole process at the system level and equipment level.

5.2 Operation management of FAO system

5.2.1 Characteristics of FAO operation management

Before discussing the operational management of the FAO system, the characteristics and changes of operating the FAO system are analyzed in the following four aspects.

(1) New coupling of system architecture. The highly integrated and deep coupling characteristics of the FAO system determine the new coupling characteristics of the operational management oriented to the use and maintenance of the FAO system. Specifically, the new coupling characteristics involve the operation control between human and system, the operational rules of man-machine cooperation and collaboration, and the coupling of position collaboration and organizational structure.

(2) New construction of management mode. A suitable new management mode is needed to realize the coordination of personnel, operational rules and FAO equipment and facilities, as well as to give full play to the potential of equipment, operators and even passengers, and provide better transportation services.

(3) New changes in operational risk. The practice on the FAO lines has proved that the safety and reliability of the FAO system are greatly improved and the operation risk is significantly reduced compared with the traditional system. However, much attention should be paid to the new and changed risks.

(4) New requirements for staff. FAO has new requirements for the cooperation and joint control among various specialties and positions (especially for dispatcher, crew, and station staff).

5.2.2 Operation management method of FAO system

Based on the operation management characteristics of the FAO system, the operation management methods can be summarized from the aspects of operation and production, safety and emergency response, and staff organization.

(1) Operation and production management for Characteristics 1 and 2. The operation department needs to decompose the overall operation objective into the relevant departments and specialties of the FAO line and formulates corresponding work plans. Besides, the relevant traffic organization and management rules are reasonably formulated according to the characteristics of different FAO scenarios. The corresponding passenger transport service system and passenger transport organization plan in line with the characteristics of the FAO line are drawn up. Based on the comprehensive performance of the FAO system, the completeness of operational rules, and the mastery of the operators’ skills, a reasonable operation and management mode should be gradually implemented in stages. The maintenance specialties are divided according to the operational requirements and interface characteristics. Further, the scope of maintenance work and cooperation mode for the specialties are determined to achieve refined management of the equipment and facilities system.

(2) Operational safety and emergency response management for Characteristic 3. It is necessary to focus on the new and transferred risks in the FAO system, and to establish a safety risk analysis and preventive control system while adhering to the policy of safe production. Additionally, the unmanned operation of the system puts forward higher requirements for emergency management, which requires an improved emergency plan system, a rapid emergency response mechanism, and an efficient emergency handling system.

(3) Staff organization management for Characteristic 4. It is necessary to adjust and optimize the operation organization structure and related position responsibilities, and build a training system that can match new requirements. The systematic basic training and the retraining required to maintain workforce capabilities should be provided to enable personnel to quickly respond to and solve problems when facing the real emergency environment, thereby reducing the impact of emergencies on normal operation.

6 Conclusion and prospects

This paper reviews the development history of the urban rail transit FAO system, and analyzes the design requirements of the FAO system based on the theory of human factor engineering. The key technologies applied in the FAO system are introduced. Furthermore, the construction and operation management methods of the FAO line are summarized based on the independent innovation practice of the FAO system.

At present, the FAO system has limitations in operation. For example, in the case of peak hours with large passenger flow, when there is no station staff, determining the timing to open and close the doors of the train is a tricky problem in daily operation. Moreover, the current FAO system still requires the participation of staff in the face of emergency response. On the basis of the FAO system, the future urban rail transit will realize standardized and networked operation. The system architecture will be more simplified, the operation organization mode will be more flexible, and the equipment computing resources and data will be utilized more reasonably. With the continuous improvement of service quality, rail transit will increasingly become the primary choice for urban residents to travel. The research of FAO technology should be brought forward by using the advanced technologies such as artificial intelligence, big data and cloud computing, which is of great significance for promoting the development of the intelligent urban rail transit system. The future development trend of FAO system mainly includes the following three aspects:

(1) Interconnected FAO system. It is necessary to form the design concept, operation organization mode, resource allocation method and safety management method of the interconnected FAO system. Based on the original FAO system, the interface adaptation is required to realize the interconnection of equipment from different suppliers on the same line and cross lines.

(2) Intelligent control of fully automatic train based on vehicle-to-vehicle (V2V) communication. The V2V communication-based architecture can be adopted to realize the FAO scenarios, which can break through the control mode of commanding trains on the ground and realize the coordinated control between fully automatic trains with the mobile vehicle as the core. Based on the technologies like multi-sensor information fusion, computer vision and deep learning algorithms, the abilities of active perception and intelligent decision-making of the train can be enabled, which leads to the intelligent control of fully automatic trains.

(3) Integrated traffic control platform based on cloud computing. Through integrating multiple disciplines such as electric power, vehicle, communication, signaling, integrated supervisory control, and foreign object detection in the FAO system, an integrated information cloud platform centered on traffic control is established to realize information exchange, resource sharing, and centralized operation and maintenance among multiple systems. It will further improve the reliability, efficiency and intelligent operation and maintenance level of the FAO system [19].