This unassuming slanted roof, house-like structure at the foot of the mountain may appear like a private residence or perhaps a garage, but really is the entrance to the second longest highway tunnel and longest combined rail and highway tunnel in North America. Located fifty miles southeast of Anchorage, near Portage Glacier, in the U.S. state of Alaska, the Anton Anderson Memorial Tunnel, also referred to simply as the Whittier Tunnel, connects the port city of Whittier on Prince William Sound to the Seward Highway. The 4,100 meter-long tunnel passes wholly under Maynard Mountain. It was built during the second World War, at the cost of $80 million, and is the first tunnel in the U.S. that allows automobiles to drive directly over the track area - a design that saved tens of millions of dollars compared to what would have cost if the tunnel was widened to allow the roadway to be separated from the track. The tunnel was named after Anton Anderson, an engineer for the United States army who played a principal role in the construction of the tunnel.

A vehicle enters the Anton Anderson Memorial Tunnel, North America’s longest combined rail-highway tunnel. Photo credit

Whittier Tunnel is just 16 feet wide and has a single lane shared by both rails and cars. Rail and road traffic are coordinated by two sophisticated computer-based systems which control the timing of vehicles entering the tunnel, spacing them for safety, and lower railroad gates when a train is approaching. Cars heading to Whittier are allowed every half hour while cars leaving Whittier can enter the tunnel every hour. In between regularly scheduled passenger trains are also accommodated.

The tunnel interior is exposed to the natural rock - only portions of the tunnel are lined with concrete and steel. The majority of the tunnel has a wire mesh attached to the ceiling to catch any loose rocks that could work out over time. Inside the tunnel there are several "safe-houses", which are small buildings that are used in case of severe earthquakes, vehicle fires, or other emergencies. The tunnel also contains several turnaround spots, which are reserved for disabled vehicles.

Fresh air is pumped into the tunnel using a combination of conventional portal fans and reversible jet fans which look like pretty much like aircraft jet engines.

The tunnel's entrance portals are designed in an A-shape, with a large, train-sized "garage door", which allows traffic in and out of the tunnel. As many as 450 vehicles can wait outside for passing through.

A southbound train exits the Anton Anderson Memorial Tunnel. Northbound vehicular traffic can be seen lining up, waiting its turn to head back through the tunnel toward the Seward Highway. Photo credit

Photo credit

Photo credit

The 2.5 mile long tunnel has eight safe houses, which can provide refuge during an emergency. Photo credit

Tunnel control operator Daniel Gutierrez monitors traffic from 60 video cameras at the tunnel control center on Thursday, June 19, 2014. All tunnel operators are also firefighters trained to respond to an accident inside the 2.5 mile long tunnel. Photo credit

Photo credit

Sources: Wikipedia / dot.alaska.gov / alaska.org