US-12 / Ford Exit Dr. South BoundCounty: Washtenaw
City/Township: Ypsilanti Twp.
Location: US-12 / Ford Exit Dr. . South Bound
Year Built: 1942 About this Bridge: The four bridges comprising the Willow Run Tri-level Grade Separation Historic District are eligible for the National Register as significant components of the expressway system developed during World War II to serve the Willow Run bomber plant. The B-24 aircraft produced at the facility were considered vital to the nation's defense. The bridges are also eligible under the category of Engineering as a creative solution to the massive volume of traffic anticipated when shifts changed at the bomber plant. The tri-level grade separations are located on a section of US-12 developed during World War II as the Willow Run Expressway. The 21-mile-long divided highway edged the Willow Run bomber plant to the north, west, and south. To the east, it merged with the 17-mile Detroit Industrial Expressway, which was also under construction during the same period. Designed to produce the massive B-24 bombers, the $47 million Willow Run plant included "its own airport, hangars, assembly building nearly a mile long, machine shop, power plant and offices." When the Ford Motor Company unveiled plans for the facility in February 1941, Michigan's highway department was confronted with a significant problem: "Here was the world's largest plant under one roof located more than 20 miles from its main source of labor." The Willow Run work force was projected to reach 100,000, mostly to be drawn from Detroit. Employee transportation was not the only logistical quandary confronting planners. A highway department survey in 1941 found that thirteen percent of Michigan's factories received all production materials by truck; over half relied on trucks to ship their finished product. Almost three-quarters of the highway department's engineering staff focused on the problems of circulation around the plant and associated access roads, a road system christened the Willow Run Expressway. As many staff left for military service, the department increasingly relied on consulting engineers and the Wayne County Road Commission. In addition, the railroads assisted with developing track-highway grade separations. Together these engineers responded quickly and creatively, designing a highway that reflected the unusual needs of the factory, such as the massive traffic movement at shift changes. Among the most innovative features of the expressway were two three-level, steel-girder grade separations. The only other structure of this type in the country was under construction at the same time on a highway serving the Pentagon in Washington, D.C. Bridges throughout the system were designed with an eye to both the speed of construction and the economy of critical materials. Concrete was used whenever possible to conserve precious steel. Lester Millard, Michigan highway department bridge engineer, observed that "this group of bridges represents one of the most complex problems in design and detailing ever completed by the Bridge Division." Working closely with the road commissions in Wayne and Washtenaw counties and with the federal Public Roads Administration, the highway department began awarding contracts for the roadway improvements in October 1941. Construction started immediately, even though the regular season for concrete work had ended two weeks earlier. Contractors improvised and innovated to keep the ground and materials from freezing. Later that winter, contracts were awarded for the remainder of the project, including construction of the final six grade separations. The speed with which one of the Willow Run tri-level grade separations was erected illustrates the urgency of the defense build-up: construction began the day after the contract was let on 11 February 1942, and the structure was completed by 1 August of that year. The unusual grade separations were mentioned in most articles about the Willow Run/Detroit Industrial Expressway system, which received significant press coverage. A 1945 article in Michigan Roads and Construction, for example, noted that "two tri-level bridges, which separate traffic in three directions, are an important part of the Willow Run Expressway." All in all, the state-of-the-art limited-access system contained a total of 43 highway grade separations, as well as two bridges and 11 grade separations. Less that a dozen of these structures survive today. This substantial attrition further increases the significance of the four bridges that form Willow Run's two tri-level grade separations. Less that a dozen of these structures survive today. This substantial attrition further increases the significance of the four bridges that form Willow Run's two tri-level grade separations.