Collision avoidance radar system for the bullet train: implementation and first results

Bullet trains greatly improve railway transportation capacity because they travel at amazingly fast speeds on specially designed high-speed railways. These trains are designed to travel at speeds as high as 400 km/h. As traveling speed increases, the ability of the emergency braking system on the bullet train has to be enhanced so that the train can stop in emergency situations such as signal failure in a railway communication system or rock slides blocking the railway. Bullet trains usually travel in two directions between two railway stations on parallel tracks. Bullet trains traveling in the same direction are supposed to run on the same track. In China, an automatic blocking technology supported by the complicated railway communication system is used to avoid collisions by keeping the bullet trains isolated from one another in different sections of the railway. However, this kind of technology is not capable of providing the driver with the exact positions of other bullet trains or of discovering obstacles on the track ahead. When a signal failure happens, a bullet train may wrongly run into a section of railway occupied by another bullet train. If the bullet train entering the railway travels faster than the bullet train ahead, a collision is likely to occur because the driver of the second bullet train does not have enough time to stop the fast-traveling train after he sees the train ahead and realizes a collision is impending. This was the main cause of 34 deaths in the "7.23" Yongwen line train crash that happened in China in 2011. In addition to the sophisticated railway communication system, it is important to equip bullet trains with a technology that will allow the drivers to monitor the condition of the railway their train is traveling on. The unique collision avoidance radar system for the bullet train presented in this article is called CA radar. The CA-radar system is designed to be mounted on the head of the bullet train, can provide the driver with real-time information about the track ahead, and can allow that driver to detect obstacles on the track. It will work well under all weather conditions, day and night, at distances of several kilometers, ensuring a final line of defense for the bullet train against collision events. CA radar is an important branch of radar technology application in civilian sectors. It has received considerable research and attention with promising results in cars [1]-[4], unmanned aerial vehicles [5]-[7], planes [8]-[10], and other transportation systems. Compared with other transportation systems, the bullet train runs on a specially designed high-speed railway with more complicated circumstances: there are always many buildings beside the track, and catenary poles with uniform spacing are installed along the high-speed railway to provide electric energy to the bullet train. The distance between the catenary poles and the track is always small, as shown in Figure 1. When designing a CA radar, several principles need to be followed. These include the following: 1. The system should be active at a range larger than the maximum breaking distance of the bullet train. A detecting range of 3 km is sufficient for the CA radar to prevent a collision, because the bullet train usually travels at a speed of 300 km/h with a maximum breaking distance of 2,700 m [11]. The system also should have high range resolution to separate items of different distances. 2. Antennas installed on the train should not increase the aerodynamic drag for the high-speed bullet train. 3. Velocity estimation should be provided for the prediction of a coming collision, and targets with different speeds should be separable.4. The azimuth angular resolution should be high enough to distinguish catenary poles near the track from another bullet train or an obstacle on the track.