Since the arrival of the first steam engine in 1881, many wagons and automobiles were involved in accidents while crossing the railroad tracks in Winslow. Dedicated on December 15, 1936, the Williamson Avenue Underpass has allowed cars and pedestrians to safely avoid the tracks, and trains to cross U.S. Highway 87, ever since. 

The Williamson Avenue Underpass was a cooperative project of the Atchison, Topeka and Santa Fe Railway, the State of Arizona, the City of Winslow, and the Works Progress Administration (WPA). A New Deal program in response to the Great Depression, the WPA cooperated with communities nationwide by employing local workers on relief to construct public works and buildings. The local men most responsible for bring­ing the WPA project to Winslow were City Engineer Frank Goodman, Chamber of Com­merce President J.A. Greaves, and Chamber Secretary Walter Lindblom.

The contract went to the R.C. Tanner Construction Company of Phoenix for an estimated $150,000 (over $3,370,000 today). The project took eight months and 70,000 WPA man-hours to remove 14,500 cubic yards of earth, pour 3,000 cubic yards of reinforced concrete, and place 180 tons of steel in the ceiling and walls.

The underpass’s architecture displays Mission Style detailing of pierced parapet walls and guardrails, curved and corbeled bulkhead brackets, and a Spanish tile-roofed corner tower. Nearby, two concrete-and-steel pylons with the word "subway" on all sides marked the location of the important crossing. (One of those pylons was found in the surrounding desert decades later and returned to the City of Winslow, which reinstalled it in its original location in August 2019.)

Over 2,000 people attended the grand opening of the Williamson Avenue Underpass on December 15, 1936, when they heard remarks by local and state officials and a performance by the Winslow High School Band. Arizona Highway Commission Chairman Shelton G. Dowell stated that, "Having seen this structure for the first time since it was completed, I want to compliment and congratulate each man, from the contractor and highest engineer to the lowest cement worker's apprentice, for having turned out such a work of beauty and engineering. I am proud and happy to be able to present this underpass to you, the Honorable Mayor of Winslow, and trust that it may always be the vital factor in the saving of lives and time that it was intended to be." The Williamson Avenue Underpass was listed in the National Register of Historic Places in 1988.