It's not a new idea. In the USA before continuous air brakes for every freight car were introduced brakemen used to walk along walkways on the roofs of the cars applying and releasing brakes as needed. In addition to good balance these brakemen needed good route knowledge to avoid low bridges and tunnels. To give them warning of such obstacles wires were strung across the track and streamers hung down to brush against the brakemen. If they felt the streamers they had time to crouch down.