The L train was supposed to shut down for repairs come April. The plan to move passengers around during that time took years to prepare, costing millions.

But it would be worthwhile, transit officials said. All they needed was 15 months with no trains in the tunnel connecting Manhattan and Brooklyn.

Then Gov. Andrew M. Cuomo stepped in.

His new plan would allow trains in the tunnel during rush hour, and less frequently on nights and weekends. How? New technology never before used in America. Presto!

Mr. Cuomo was praised by some as a subway savior. Others wondered why the eggheads running the trains didn’t think of this in the first place.

But it turns out — they had!

According to documents obtained by The Times, in 2014, transit officials rejected a similar idea — which involved mounting cables on the side of the tunnel walls — because of concerns about safety and reliability.