Why is there a light flashing on the roof of the high-speed train?

This is a high-speed camera called "Vehicle Catenary Operation Status Detection Device" ("3C" for short).

This is a pantograph surveillance camera that allows on-board mechanics to monitor the working status of the pantograph in real time.

High-speed railways have different regulations in different countries and times. The China National Railway Administration defines it as: newly-built passenger dedicated railway lines designed to operate EMU trains with a speed of 250 kilometers/hour (including reservations) and above, and with an initial operating speed of not less than 200 kilometers/hour. Features: Newly built, with a speed of not less than 250 kilometers per hour and passenger specificity. Difference: In 1962, the early European organization, the International Union of Railways, classified old lines with a speed of 200 kilometers per hour and new lines with a speed of 250 to 300 kilometers per hour as high-speed railways; in 1985, the Geneva Agreement made new provisions: new passenger and freight linear high-speed railways The speed of the newly built passenger dedicated high-speed railway is more than 250 kilometers per hour. ?

China is divided into three levels: high-speed railways - express railways - ordinary railways. The high-speed railway level is higher than the national railway level I and is used for express railways and backbone ordinary railways. China's high-speed railways generally use ballastless tracks and high-speed EMUs (G-prefix trains). Initially, CRH2C and CRH380 series are used exclusively for high-speed railways.