On a modern CTC dispatched line, like the one in the video more than likely is, the track inspector would get "Track and Time", by which the DS would establish limits between two Control Points (Dispatcher controlled signals) such as betweeen "CP Abajo and CP Rio Bravo".
Or... He can perform inspections via Lone Worker (watchman), in which he would have someone dedicated to watching for trains coming in either direction not performing any other duty. Though with this method, you're given a chart showing the minimum sight distance needed to foul the track (80MPH is upwards of 1700+ feet),
William Diehl... \M/( >.< )\M/
-Albuquerque
Big Diehl Photo <-Photos and Books For Sale, or Like it on Facebook.