Where should I insert the red card for railway blockade construction?

During the upstream construction, it is inserted behind the upstream track construction personnel and more than 20 meters in front of the no-go train. If it is in the downlink, the insertion direction is opposite to the uplink.

The red card is a rectangle with a length of 50 cm, a width of 30 cm and a black border of 3 cm. The height of the red card is 60 yuan, and the steel bottom is splayed. The function of the splayed fork is to firmly insert the ballast into the middle of the line.