Just one? In Boston, years ago, a candidate ran radio ads complaining that it took three people to change a light bulb in MBTA system. Supervisor, guy to hold the ladder, and the guy doing the actually work.
If it was in a subway tunnel itself, I could see at least two people for safety reasons.
But what about the inspector to verify that the work was done to spec? (Believe me, I know of which I speak, hence my Freeper name ;-)