Passengers travel on a train with the "smart train passenger service system" in Beijing, capital of China, on April 2, 2020 . The "capital smart subway" scientific research project is currently tested on Beijing Subway Line 6. The system uses a large number of new technologies to inform passengers in advance of the location of the "smart train," the current crowd levels of carriages, strong or weak air conditioning in carriages and other information. (Xinhua/Zhang Chenlin)
