At certain parts, the road was too narrow for wagon teams to pass each other; the slope into which it was cut had a maximum grade of seventy-five percent, and falling over the side meant a drop of 400 feet (120 m).

The present road is four and one half miles long, its grades are too steep for heavy hauling and the bluffs around which it twists adds to its perils.The tunnel was constructed by the U.S. Army after plans were made in late 1915 to expand Fort Barry.

[8] The tunnel was listed as a contributing structure for the Forts Baker, Barry, and Cronkhite Historic District on December 12, 1973.

Workers sealed cracks in the vintage concrete to reduce seepage, repaved the road, replaced water and sewer lines, and installed energy-efficient LED lighting.

Prior to the 2017 rehabilitation, the tunnel was the second-largest consumer of power in the entire Golden Gate National Recreation Area (after district headquarters in San Francisco).

[12] During the shutdown, traffic was rerouted to Conzelman Road, a coastal route which is popular among tourists for scenic views of the Golden Gate.

It is cut through serpentine rock and as completed in 1918, was supported with a timber structure and featured a macadam road with cobblestone gutters.

The rebuild also added galvanized iron and trenches to try to keep moisture out, along with barbed wire fencing to prevent cattle from entering the tunnel.

[3] The reconstruction in 2017 cost an estimated $7 million, and involved the injection of 45,000 pounds (20,000 kg) of polyurethane resin to stop leaks along with 900 short tons (820 t) of new paving.

[12] Prior to the 2017 work, the stalactites that had formed from the water seeping through the rock and concrete were removed and displayed at the Exploratorium in San Francisco.