Manhattan Island is linked to New York City's outer boroughs and New Jersey by several tunnels as well. The Lincoln Tunnel, which carries 120,000 vehicles a day under the Hudson River between New Jersey and Midtown Manhattan, is the busiest vehicular tunnel in the world. The tunnel was built instead of a bridge to allow unfettered passage of large passenger and cargo ships that sailed through New York Harbor and up the Hudson River to Manhattan's piers. The Holland Tunnel, connecting Lower Manhattan to Jersey City, New Jersey, was the world's first mechanically ventilated vehicular tunnel when it opened in 1927. The Queens-Midtown Tunnel, built to relieve congestion on the bridges connecting Manhattan with Queens and Brooklyn, was the largest non-federal project in its time when it was completed in 1940. President Franklin D. Roosevelt was the first person to drive through it. The Hugh L. Carey Tunnel runs underneath Battery Park and connects the Financial District at the southern tip of Manhattan to Red Hook in Brooklyn.
The Holland Tunnel opened in what year? (If the question is unanswerable, say "unanswerable")
1927