Fleur Drive in the City of Des Moines is one of the heaviest traveled thoroughfares in the entire City (2016 Count = 33,200). It connects a large portion of the south side to the downtown as well as the street on which the Des Moines International Airport is located. On the near south side of the downtown, Fleur Drive traverses two large parks: Gray’s Lake Park on the east and Des Moines Water Works Park on the west. While Gray’s Lake Park has been developed for some time, Water Works Park remains largely undeveloped.
Water Works Park encompasses an area larger than Central Park in New York City. To take advantage of this under utilized asset, the Des Moines Water Works Park Foundation (Foundation) was formed to develop this jewel in the heart of the metropolitan area. The Foundation retained RDG, USA to develop a masterplan to create spaces within Water Works Park for all to enjoy.
To that end, one need was to eliminate the at-grade crossing for pedestrian/trail users at the Fleur Drive intersection with George Flagg Parkway at the south side of both parks. While Flagg Parkway is to the west, the entrance to the Gray’s Lake Marina is to the east. Needless to say, at this busy location something had to be done to improve the safety for walkers, runners, and cyclists.
Two concepts were developed for this crossing of Fleur. Either construct a trail bridge up and over or build an underpass of Fleur Drive. After public input from several meetings, the decision was made to develop the underpass concept. At the recommendation of the City, Calhoun-Burns and Associates was then brought to the table to develop the underpass idea.
After several meetings of the City, Des Moines Water Works and the Foundation, the optimum structure type was determined to be a precast concrete arch. It emulated the arch concept of numerous other arch structures throughout the City. In addition, in mimicked the concept of an arch bridge that one might find in Central Park.
As the City would ultimately own the structure, before design of the underpass could begin, a 28E Agreement between the City and the Foundation had to be executed. A stipulation by the City of the Agreement was that Calhoun-Burns would be the lead design firm to develop the project with RDG as the subconsultant design firm. Design work began immediately following execution of the Agreement. Calhoun-Burns was responsible for the structural design and plan development while RDG was responsible for the aesthetic elements and civil design of the project.
For constructibility, there are three primary reasons precast concrete was selected. First, it was well suited for staged construction. The high volume of traffic on Fleur Drive did not allow for closure and a practicable detour. Second, the use of precast concrete minimized the closure of each stage and all four lanes were fully open to traffic in the fall of 2019. And third, the numerous utilities through the site including natural gas, overhead electric, underground electric, a dedicated fiber optic line for the FAA, water, and storm sewer.