Which of the following is a requirement for riding on a flat car?

Riding in a seated position facing forward is important for safety and stability while on a flat car. This position helps the rider maintain balance and minimizes the risk of falling off the car. Additionally, facing forward allows the rider to better see the direction of travel and be aware of any potential hazards ahead, which is crucial in a moving train environment.

Other choices suggest unsafe practices: riding on the edge of the car increases the likelihood of falling, riding without a handhold can lead to losing balance, and extending feet beyond the car poses a serious risk of injury. Therefore, seated and facing forward is the safest and most compliant method for riding on a flat car.