A helicopter could up to inspect the full lengths of the line each day before they open at rush hour.
Who will inspect the complete set of secondary zip lines for emergency response teams, though?
(inside joke, you have to know Endgame's past history of absurd ideas/suggestions)
WHO in their right minds would under-write the liability issues when those lines break? I can see them measuring now....."well the line broke more on the Brooklyn side then the Manhattan side, so the Dodger's will have to pay for THIS one".
A helicopter could go up to inspect the full lengths of the line each day before they open at rush hour.