Which tunnel do A and C line trains utilize into and out of Manhattan?

The correct answer is the Cranberry Street Tube. This tunnel is vital for the A and C line trains as it allows them to travel under the East River, connecting Brooklyn to Manhattan. The Cranberry Street Tube is specifically designed to accommodate the subway system, providing a reliable passage for transit services.

In contrast, the Wallenberg Tunnel is not a designated route for subway trains, primarily serving vehicular traffic. The Hudson River Tunnel primarily accommodates Amtrak and the PATH train service, making it unsuitable for the A and C lines. The Lincoln Tunnel, known for vehicular travel between New Jersey and Manhattan, is also not part of the subway system. Thus, the Cranberry Street Tube is the only option that serves the A and C line trains directly, ensuring their continuity and operational effectiveness between these two boroughs.