Abstract: This paper introduces the composition and functions of a tunnel monitoring system, and elaborates on the characteristics of industrial Ethernet, area controller, tunnel ventilation subsystem, and tunnel lighting subsystem. Keywords: Tunnel monitoring system; Industrial Ethernet; Area controller With the development of China's expressways, especially the implementation of the new road network in the "National Expressway Network Plan," a number of long and extra-long tunnels have been built. The new road network consists of 7 radial lines from the capital, 9 north-south longitudinal lines, and 18 east-west transverse lines. China will invest 2 trillion yuan over 30 years to form an 85,000-kilometer national expressway network. According to the latest statistics released by the Ministry of Transport, in 2004, there were 2,495 highway tunnels nationwide (excluding data from Hong Kong, Macao Special Administrative Regions, and Taiwan Province), with a total length of approximately 1,245,600 meters; among them, there were 33 extra-long tunnels, totaling 126,300 meters; and 299 long tunnels, totaling 493,300 meters. Highway tunnels differ from railway tunnels, requiring safe and user-friendly lighting and ventilation facilities, and even more importantly, a complete and comprehensive emergency response plan. With the sustained and rapid development of China's economy, the volume of transportation has increased dramatically in recent years. When vehicles pass through tunnels in dense or slow-moving traffic, it can lead to an increase in pollutants (such as CO) and a decrease in visibility. Highway tunnels are special structural sections within the entire road segment. Due to their small space and high degree of enclosure, the environment inside the tunnel can deteriorate rapidly in the event of a fire, accident, or traffic congestion, directly affecting the health and safety of drivers and passengers. Therefore, higher requirements are placed on tunnel monitoring systems. 1. Structure of Tunnel Monitoring Systems A highway tunnel monitoring system is, to a certain extent, a closed-loop control system, including environmental monitoring and traffic control systems, lighting control systems, ventilation control systems, fire alarm systems, CCTV systems, fire control systems, emergency telephone communication systems, and power monitoring systems. Typical characteristics of tunnel engineering include long distances, large scale, numerous stations, and many communication targets. Highway tunnels are generally separate for upstream and downstream traffic, with twin tunnels and one-way traffic on two lanes. Various equipment such as lighting, ventilation, area control, fire protection, drainage, emergency telephones, communication, and traffic guidance devices are installed inside the tunnel to ensure safe and normal passage. Therefore, proper scheduling, monitoring, and surveillance of these devices are essential for the safe and smooth operation of the tunnel, especially in accident situations, where they are crucial for ensuring the safety of personnel and equipment. The industrial Ethernet network topology of the tunnel monitoring system is shown in Figure 1. This network communicates via a 10Mb/100Mb fiber optic self-healing ring network of the area controller. Because it uses a self-healing fiber optic redundant ring network, even if one end of the fiber is disconnected, all controllers in the fiber optic redundant ring network can still communicate normally through the other end, ensuring communication reliability. In addition, besides collecting information from each substation, the area controller also controls and collects information separately from the tunnel's ventilation, lighting, and traffic guidance equipment (variable message signs, variable speed limit signs, cross passage signs, lane indicators, etc.), traffic detection equipment (such as vehicle detectors), environmental monitoring equipment (such as CO detectors, transmittance detectors, visibility detectors, etc.), and lighting detection equipment. The control room server also includes a BT repository with functions for searching and storing Torrent files from major BT publishing websites, facilitating browsing and querying. This software seamlessly integrates BT torrent download functionality, allowing direct download of BT torrents and subsequent opening of associated BT download software. It localizes torrent file information, downloading the latest torrent files from relevant BT websites to your local hard drive for easy browsing. It allows previewing detailed file information; hovering the mouse over a file name in the data list for a specified time will automatically display a tooltip showing detailed information. It features data sorting capabilities, allowing sorting by addition time, file size, file name, current number of torrents, number of connected users, etc. A search function is included; simply enter search keywords and press Enter to find desired movies, TV series, variety shows, and anime. The download function is convenient; simply double-clicking a file name in the data list downloads the corresponding torrent file. After downloading, if BT download software is installed on your computer, it will automatically run and open the torrent file directly. It is truly legal; large files are often large audio files that take up a lot of space, and many of these are TV programs or pirated movies, which BT excels at distributing. BT will make it possible for everyone to become a broadcasting company. You no longer need a broadcasting network to showcase your products. Just compress the TV program into a computer file, add the BT protocol, and put it on the Internet. Users can simply click the link, download it, and watch it at any time. According to authoritative sources, as producers of all sizes take advantage of this low-cost distribution channel, a large number of new TV programs will be launched. In August 2005, the British Broadcasting Corporation (BBC) announced the MyBBCPlayer project. This system uses a similar P2P protocol, allowing viewers to legally download some BBC TV programs. Mark Pesce, an interactive media lecturer at the Australian Academy of Cinema and Broadcasting, said that BT will not only change the way television is distributed, but also the way TV programs are produced. BT is bound to continue to develop and will change the online media industry. It is like an Internet revolution. It connects with the upper control center via the Internet. The cross-sectional distribution of equipment in the tunnel is shown in Figure 2. 2 Functions of the tunnel monitoring system (1) Determine the speed limit value at the tunnel entrance and other relevant traffic information based on visibility parameters. The visibility parameters in the tunnel are divided into several levels, each corresponding to a different speed limit value, and the parameters can be flexibly modified in the software. For manually released text information, a certain number of commonly used contents will be listed for operators to select. (2) Various tunnel maintenance and accident information sent by emergency calls, patrol cars, and maintenance departments can be manually input, including the occurrence time and termination time of the accident, location, type, accident detection method, monitoring measures used in the accident handling process, accident description, etc. (3) The tunnel lighting will be automatically controlled by the tunnel management station based on the parameters detected by the light intensity detector and the tunnel operation status at this time (normal, blocked, fire, etc.). (4) The traffic conditions in the area can be confirmed by monitoring and recording through cameras installed at the tunnel entrance and inside the tunnel. (5) The working status of the tunnel ventilation system and lighting system can be monitored. (6) The environmental conditions of the area can be detected by CO/VI detectors installed in the tunnel, and the necessary parameters can be provided for the corresponding control of the ventilation system. (7) Utilize vehicle detectors to detect parameters such as traffic volume, average speed, and occupancy rate. Through calculation, traffic congestion, blockage (several levels), accidents, or vehicle malfunctions can be determined, and alarms can be triggered. (8) Utilize automatic fire detectors and manual alarm buttons installed in the tunnel to automatically and manually detect and upload fire information in the tunnel. (9) When a fire, traffic congestion, or emergency telephone alarm is detected in the tunnel, the corresponding camera display can be automatically switched and video recorded. (10) After confirming the event status in the tunnel through the camera, the system can automatically prompt the control mode. After manual confirmation, information can be released, or the control command can be manually reset. (11) The system has a unique control scheme corresponding to different event types and locations. (12) Information can be released through facilities such as variable message signs (outside the tunnel), small variable message signs (inside the tunnel), traffic lights at the tunnel entrance, lane indicators, cross passage indicators, and wired broadcasting systems. (13) In the event of traffic abnormalities or accidents, the duty officer can dispatch patrol vehicles and highway management personnel for auxiliary control via command telephone, and can adjust the mainline traffic volume by adjusting the number of toll lanes opened at toll stations adjacent to this tunnel. (14) For the automatic provision of control commands, the duty officer shall confirm before issuing them manually. (15) The working status and equipment fault information of the following equipment will be displayed in real time on the monitoring computer and the monitor wall, and the content being displayed by the issuing equipment can be displayed: manual alarm button, automatic fire detector, vehicle detector, variable message sign, small variable message sign, variable speed limit sign, emergency telephone, CO/VI detector, light intensity detector, tunnel entrance traffic lights, lane indicator, cross passage indicator, etc. (16) The tunnel management station can control, switch the display and record the tunnel images, and ensure that the full-length monitoring function of a single tunnel can be realized when an abnormality occurs in the tunnel. When a fire occurs in the tunnel, the video control matrix can automatically switch the images of nearby cameras to the monitor of the control console according to the location of the fire alarm point, and trigger the recorder to record automatically. (17) In the event of a fire, traffic anomaly, or abnormal environmental conditions in the tunnel, the operation of the traffic guidance system (including traffic lights at the tunnel entrance, lane indicators, cross passage indicators, variable speed limit signs, variable message signs, and small variable message signs), ventilation system, and lighting system at the tunnel will ensure the safe operation of tunnel traffic. All signal signs are interlocked and there will be no contradictory signal displays, thus achieving the safety control function. (18) The tunnel management station will automatically transmit some necessary data, images, and alarm information to the toll monitoring area center in real time, including information from vehicle detectors, emergency telephones, and the content published on variable message signs. (19) The tunnel management station can receive various control commands and system parameter information issued by the toll monitoring area center. In addition, the tunnel management station can receive network clock time issued by the toll monitoring area center and can automatically correct the computer time to ensure the uniformity of the computer system clock. (20) The tunnel management station will upload image signals to the toll monitoring area center. (21) The monitoring system scheme, equipment, software, database structure, and format will fully consider the situation of the toll monitoring area center and the provincial monitoring system to achieve equipment networking and software compatibility. 3. Industrial Ethernet and Area Controller in the Tunnel Site A substation control room is provided, containing control cabinets, power cabinets, PLCs, power supply circuits, etc., which control related lighting, ventilation, and area control equipment. Each PLC collects information from the lighting, ventilation, and local control systems, and performs corresponding actions according to the set programs and instructions from the host computer. The collected information is transmitted to the central computer in the control room via a 10Mb/100Mb fiber optic Ethernet redundant ring network, achieving network connectivity. In addition, real-time information from various tunnel devices is aggregated on the server in the tunnel monitoring center. Therefore, the local controllers can not only quickly exchange real-time data and collect data, but also receive and execute instructions from the host computer. Operation commands can be issued to any device in the field (lighting, ventilation, local controllers) through the server. For this reason, a PLC is selected as the area controller for the tunnel's main controller, as it has high-speed information exchange capabilities and good control functions. Each PLC is equipped with an RS-485/RS422 or RS-232 communication port for connection to instrument control devices such as multi-parameter intelligent transmitters, speed limit controllers, and variable message sign controllers. The serial communication data protocol varies depending on the manufacturer and the equipment. These protocol differences make communication between devices from different manufacturers very difficult, even if they share the same electrical standards. PI~ solves this problem through easily created protocol macros for matching the protocols of connected devices. These macros eliminate the need for developers to write dedicated communication programs for communication with third-party devices. In principle, PI~ can communicate with any device with an RS-232c, RS-422, or RS-485 interface. In this control system, each area controller for controlling lighting, ventilation, power, and traffic equipment uses an independent control program. Two area controllers are each equipped with a human-machine interface touchscreen. Monitoring and control of lighting, ventilation, power, and traffic monitoring can be achieved through the PLC and touchscreens. The central computer in the control room communicates with the upper-level control center via Ethernet. Fiber optic Ethernet redundant ring network is an important network for PLCs. It supports automatic data exchange between PLCs and between PLCs and the host computer. It can also use information services for programmable data transmission. The tunnel monitoring system uses fiber optic Ethernet redundant ring network for data communication. 4. Ventilation Control Subsystem The ventilation control subsystem controls the number of operating fans, airflow direction, and operating time based on detected transmittance, CO concentration data, and traffic volume data. This achieves energy-saving operation and maintains the optimal lifespan of the fans. In the event of a fire, it performs appropriate smoke extraction according to different locations to ensure tunnel safety and a comfortable operating environment. Generally, the ventilation control subsystem of a tunnel can be controlled in four levels: First, the monitoring center (automatic control, remote manual control); second, the tunnel monitoring room (automatic control, manual control); third, the tunnel substation (manual control); fourth, the ventilation fan switch box (manual control). Under normal circumstances, the fan control switch in the tunnel substation is set to the "automatic" position, and the monitoring center monitors the ventilation control subsystem and automatically completes its various functions. In case of failure or when necessary, the system should maintain normal operation at any of the first three levels after switching. When maintenance and testing of ventilation equipment and the ventilation control subsystem are required, manual control is implemented from the tunnel monitoring room, the substation, and the ventilation fan switch box. The ventilation control subsystem consists of a monitoring center workstation, a tunnel equipment room area controller, a ventilation control cabinet, tunnel fans, CO detectors and transmittance detectors, connecting cables, and power cables. The CO detectors and transmittance detectors are located inside the tunnel and are used to detect CO concentration and visibility. Data is collected by a local controller, and the monitoring system compares the detected data with standard values ​​to control the start and stop of the fans. The ventilation system's ventilation control cabinet, located inside the tunnel, enables local manual control and reserves conditions for remote control and signaling. The monitoring system has a local controller in the tunnel substation. It is connected to the ventilation control cabinet via relay contact outputs to ensure remote control of the fans. Each individual tunnel is controlled independently to minimize mutual interference. The automatic control system for the ventilation fans in the monitoring system groups two fans on a cross-section together for control. The ventilation system returns status signals for each fan, including forward rotation, reverse rotation, stop, and fault signals. Electromagnetic isolation measures are in place between the input and output. 5. Tunnel Lighting Control Subsystem The tunnel lighting control subsystem controls the tunnel lighting system based on detected light intensity data inside and outside the tunnel, traffic volume changes, and day/night conditions. It adjusts the lighting at entrances and exits and inside the tunnel to ensure traffic safety and achieve energy-saving operation while meeting lighting requirements. It also monitors the status of the lighting and lighting control equipment inside the tunnel. The tunnel lighting control subsystem consists of a monitoring sub-center computer, a local controller in the tunnel equipment room, a lighting control cabinet, tunnel lighting fixtures, and connecting cables. Both the monitoring sub-center computer and the local controller can perform lighting control. In case of communication failure between the tunnel and the monitoring sub-center, operation can be performed directly on the local controller to ensure normal tunnel operation. The lighting system is equipped with lighting control cabinets and other equipment inside the tunnel, enabling local manual and automatic control. It also reserves the conditions for remote control and signaling of monitoring devices, providing relay contacts for controlling each lighting circuit. The monitoring system has a local controller in the tunnel substation, directly connected to the relay contacts of the lighting control cabinet to ensure remote control of the lighting. Each tunnel is controlled independently to avoid mutual interference. Lighting is divided into three levels: Level 0 is daylight lighting, basic lighting, no control; Level 1 is daylight lighting and dusk lighting; Level 2 is daylight lighting, dusk lighting, and daylight lighting. [b]6 Conclusion[/b] Currently, tunnel monitoring systems are complex engineering projects. Considering that most of the core equipment of domestic tunnel monitoring systems still relies on imports, some control methods are still copied from foreign systems, tunnel equipment markings are unreasonable, and contingency plans for handling tunnel anomalies are not yet mature, in-depth research on tunnel monitoring systems, especially on extra-long tunnels, is an urgent problem to be solved. Its research results will have a significant impact on my country's economic development and on protecting the lives and property of the nation and its people.