the answer is 14.5 miles
The Seikan Tunnel is 14.5 miles long, being one of the longest tunnels in the world.
The present Cascade Tunnel is 7.79 miles long. The original Cascade Tunnel was 2.63 miles long.
The Earth's largest railroad tunnel is the Seikan Tunnel in Japan, which is over 33 miles long. When the Gotthard base tunnel in Switzerland is opened in 2016, Seikan Tunnel will be the second longest.
The world's longest railroad tunnel is the Seikan Tunnel, it is 33.49 miles long.
The Seikan Tunnel connects the Japanese islands of Honshu and Hokkaido and is 33 miles long.
It will be the 34 mile long St Gotthard beneath the Alps, Switzerland, when the tunnel opens in 2017. Until then, the Seikan Tunnel in Japan at 33 miles long
7.79 Miles
The longest under ocean tunnel is the Seikan Tonneru. It is an underwater railway tunnel in Japan. It has a 14.5 mile long portion under the sea bed. The track level is 330 feet below the sea bed.
It is located beneath the Tsugaru Strait in Japan, and is 53.85 KM (33.46 MI) long. 23.3 KM (14.5 MI) is located under the seabed. It opened on March 13, 1988. It not only is the longest tunnel, it also is the deepest train tunnel in the wold. However, watch for the completion of the Gotthard Base Tunnel in Europe to take over the record sometime around 2018.
Alas, no. There are several longer. The longest of all, the Paijanne water tunnel in Finland, is a water supply tunnel so probably doesn't count. The Seikan tunnel in Japan carries a narrow-gauge railway and is 33.5 miles long. The Channel tunnel is certainly the longest full-size railway tunnel at 31.3 miles. However, those crafty Swiss are currently at work under the Alps, and the Gotthard Base tunnel (also a standard gauge railway) will be 35.5 miles long, a clear winner.
It may be l4 miles. the Trans-Hudson ( Goddard) tunnel of the former PRR which will be l00 next year, is probably the longest subaqueous tunnel of it s type - and is rated for 80 MPH operation of heavy duty locomotives, not subway cars. The Goddard is l5,600 feet long or about 2.95 miles and some change- try it on a calculator. it has never been as much in the public eye as the automotive vehicular tunnels, the Holland and Lincoln.The Cascade tunnel ( which has an automatic ventilating system installed in the past 30-odd years with remotely controlled tunnel doors ( also keeping out vandals) and ventilation pumps turned on by approaching pressure waves of locomotives is a massive engineering feat, but is an intermountain ( name defines itself) tunnel and not a subaqueous ( Under water) type, the latter much more challenging to the engineer.
Long Dock Tunnel was created in 1860.