Railways are an important component of the Chinese transportation infrastructure and play a vital role in economic development. However, the country’s vast territory and complex and diverse terrain pose challenges to safe rail operations. Especially in the mountains of southwest China, railways are prone to hazards caused by foreign objects on the tracks, such as rockfalls. For example, on March 30, 2020, a passenger train from Jinan to Guangzhou was derailed because a landslide had affected the tracks, resulting in many injuries.

Figure 1 Train derailment on March 30 (Photo by Li Ga, a news reporter )

In addition to foreign objects on rail tracks caused by geological hazards, humans and animals can also wander onto train tracks.  The frequent intrusion of foreign objects on railway tracks severely affects the safe operation of railway systems. The timely and accurate detection of foreign objects and the triggering of corresponding alarms are crucial to railway safety.

Conventional foreign object intrusion monitoring systems for railway tracks feature dual power grids, optical fiber vibration sensing, and video monitoring. However, due to the lack of hardware capabilities, these systems cannot position foreign objects, their detection efficiency is low, and the false alarm rate and the missed detection rate are high. Lidar has been a success in the foreign object detection field due to its excellent detection capabilities and environmental adaptability. Livox assisted in the "Foreign Object Intrusion Detection Solution for Railway Tracks" solution. Livox provides a detailed introduction of the role of lidar in this solution. This solution has been implemented in the automated monitoring project for rockfall reduction for several railway lines.

Figure 2 Foreign object intrusion detection solution for Yuhuai Railway Lines: Integrates lidar, a camera, and a processing unit

Benefits of the Foreign Object Intrusion Detection Solution

The solution integrates various hardware devices, such as a lidar unit, a dome camera, a processing unit, and a headlight.

This solution allows you to obtain the 3D information of foreign objects, compensating for problems convention solutions have in detecting the size, depth, location, and other information of foreign objects. In addition, this solution does not depend on ambient light, avoiding some common issues with conventional lighting equipment. For example, conventional solutions attract moths, which can cause a high false alarm rate due to the limitations of visual-only solutions.

Figure 3 How Foreign Object Intrusion Detection on Railway Tracks Works

In this solution, the lidar is first used to extract the track surface from the scanned point cloud in the valid monitoring area. Inter-frame matching is performed for each frame when there are objects longer than 20 cm on the track surface. The differences between frames are analyzed to locate obstacles and calculate the distance between obstacles and the lidar. Then, the lidar reports the obstacle information to the dome camera and instructs the camera to rotate and focus on the foreign object and take a photo with flash. After the object is recognized from the image, the object is fed back to the monitoring center, and the personnel in the monitoring center checks whether the object is a foreign object.  In addition, the lidar can check whether the obstacle is static based on its distance to the object. In theory, only a static object that stays still for more than 15 seconds is recognized as a foreign object.

Figure 4 System on-site test

The Tele-15 is used as the main lidar, and Avia is used to compensate for the blind spots in different scenarios. Tele-15 supports long-range detection and highly dense point clouds. With 10% reflectivity, Tele-15 can measure objects at a distance of 320 m and even up to 500 m. The ultra-high point cloud density is adept at small object detection, allowing you to detect a pedestrian at a distance of 300 m and generate a point cloud with 12 points within 100 ms.

In roadside static scenarios, such as prewarning of foreign object intrusion, accurate prewarning is more important than the response time. The system leverages the unique non-repetitive scanning method of Livox lidar. As the scanning time increases, the number of points in the point cloud also increases. For example, 107 points can be detected for a pedestrian at a distance of 300 m within 1 second. Point clouds with higher density help the system accurately detect and recognize objects. 

FIgure 5 Left: Point cloud for a pedestrian at a distance of 300 m within 100 ms. Middle: Point cloud for a pedestrian at a distance of 300 m within 1 second. Right: Point cloud for a pedestrian at a distance of 100 m within 1 second

Below is a point cloud video of a single Tele-15 lidar monitoring the safety of a trackside section, which can still detect small objects as small as 20cm*20cm in size at a distance of 200 meters.

Accurate warning is the key

In addition, only a small amount of data needs to be transmitted in this solution, simplifying data transmission and analysis. The non-repetitive scanning capability provided by Livox Tele-15 and Avia greatly increases the monitoring efficiency in railway scenarios, and reduces the false alarm rate and the missed detection rate. After the solution was applied to Yuhuai Railway Lines, no false alarms or missed detection occurred, and normal objects on the railway tracks could be clearly distinguished from intruding foreign objects. No alarms are generated when a train passes a railway track without foreign objects. In comparison, when a member of the staff walked on the railway track, the foreign object intrusion detection system was triggered, transferring more accurate information to backend personnel.

This efficient and stable foreign object intrusion monitoring system was developed by integrating the advantages of lidar and conventional cameras. The system improves the accuracy of foreign object intrusion detection, making it of great social and economic significance in ensuring safe railway operations. Moreover, Livox hopes to continuously release cost-effective lidar products to reduce the overall cost of the solution. This way, the state-of-the-art solution can be applied to more miles of track and prevent more accidents.