The Anton Anderson Memorial Tunnel (often referred to simply as the Whittier Tunnel) is a tunnel through Maynard mountain in the U.S. state of Alaska. It links the Seward Highway south of Anchorage with the relatively isolated community of Whittier a port for the Alaska Marine Highway. It is part of the Portage Glacier Highway and at 13,300 feet (4,050 m), is the second longest highway tunnel and longest combined rail and highway tunnel in North America.
The original tunnel was completed in 1943 and used for railroad traffic. In the mid-1960s, the Alaska Railroad began offering a shuttle service for automobiles, similar to Amtrak's Auto Train. Amtrak's Auto , which allowed vehicles to drive on to rail cars to be transported between Whittier and the former town of Portage. As traffic to Whittier increased, the shuttle became insufficient, leading in the 1990s to a project to convert the existing railroad tunnel into a one-lane, combination highway and railroad tunnel. Construction on this project began in September 1998, and the combined tunnel was opened to traffic on June 7 2000.
As eastbound traffic, westbound traffic, and the Alaska Railroad must share the tunnel, rail and road traffic are coordinated by two sophisticated computer-based systems: the Tunnel Control System and the Train Signal System. As reflected on the Alaska Department of Transportation Tunnel Website, it is now considered "North America's longest railroad-highway tunnel." The tunnel held the title of the longest road tunnel in North America (at nearly 2.5 miles [4 km]) until completion of the 3.5 mile (5.6km) Interstate 93 tunnel as part of the "Big Dig" project in Boston, Massachusetts. It was a 2001 recipient of an Outstanding Civil Engineering Achievement Award from the American Society of Civil Engineers.