By: Greg Horn, P.E., and Steven T. Hague, P.E., S.E.
In downtown St. Louis, I-55, I-70, I-64 and U.S. Rte. 40 converge at the 42-year-old Poplar Street Bridge, creating a choke point that snarls traffic throughout the day and racks up accidents at three times the rate for similar structures.
The bridge, which crosses the Mississippi River to connect East St. Louis, Ill., with St. Louis, never was intended to carry the 120,000 cars that make their way—albeit slowly—across the span each day.
The problem already was becoming apparent almost two decades ago, when Missouri and Illinois officials began discussions to determine how to address the congestion. By 1997, they had completed an environmental impact study and selected a location for a pair of new four-lane, side-by-side river bridges. The project obtained a Federal Highway Administration record of decision to proceed in 2001, and the East-West Gateway Council—designated by Missouri and Illinois state and federal agencies as the bi-state area’s metro planning organization—designated the new bridge as one of its top two priorities.
Despite these successes, the project still lacked the federal dollars needed to fund at least half of the cost. Although $239 million in federal funding—the largest single amount ever granted to construct a U.S. bridge—was awarded for the project in the 2005 federal transportation bill, the price of the envisioned project had escalated to between $1.8 billion and $2.2 billion, making it too costly to move forward.
The Missouri and Illinois departments of transportation, owners of the project, retrenched, considering several options to reduce costs and gain additional funding, including public-private partnerships and the merits of building a new structure adjacent to the Martin Luther King Bridge, which connects the three interstates with the downtown streets of St. Louis. Last year, these leaders ultimately determined that the original project goals could be accomplished cost effectively by building the bridge in phases.
Attracting Poplar crowd
Design and environmental impact studies are under way now for the project’s first phase: the new Mississippi River Bridge, a four-lane, operationally independent structure that will carry two lanes of rerouted I-70 traffic in each direction and have a life expectancy of 100 years. To be built one mile north of the Poplar Street Bridge, in the same location identified as optimum in 1997, the span will relieve 11% of the traffic demands from the Poplar Street Bridge. It also will remove 45% of the traffic from the Martin Luther King Bridge. Initially expected to carry 60,000 cars each day, the new bridge’s 83-ft gutter-to-gutter width will allow re-striping for three lanes of interstate traffic in each direction as transportation demands continue to increase. The design also will allow for construction of an adjacent, four-lane bridge in the next 20 to 25 years.
In addition to the Mississippi River Bridge, which has an overall length of 7,742 ft, the design-bid-build project includes:
- A partial Missouri-side North I-70 interchange, connecting to I-70 as well as to the local street system via Cass Avenue;
- Improvements at the I-55/I-64/I-70 Tri-Level Interchange in East St. Louis to allow direct connections to and from both I-64 and I-55/I-70 in Illinois; and
- Construction of a roadway connecting the existing I-64/I-55/I-70 interchange with the new bridge.
The $640 million total program cost includes $306 million for the bridge and approaches, $264 million for the new roadway connections in Illinois and $70 million for the new roadway connections in Missouri. Along with the $239 million in federal funds, Illinois and Missouri are contributing $313 million and $88 million, respectively, to construct the first phase.
Working in confidence
With funding and an affordable plan in place—and because market factors tend to elevate costs the longer a project takes to design and build—the Missouri and Illinois departments of transportation have established a tight timetable, setting a goal for opening the cable-stayed Mississippi River Bridge and all other pieces of the project by January 2014. To reduce costs, the two DOTs prequalified four contractor teams for the cable-stayed bridge, giving these contractors direct input into the bridge design through a unique alternative technical concept process.
Through this procedure, each contractor is working with design firm HNTB, providing confidential, cost-saving ideas based on individualized technology and expertise. In addition to its baseline design—on which another set of contractors will be able to bid—HNTB is developing proprietary designs that incorporate each of the prequalified contractors’ approved concepts. HNTB will submit both the individualized and the baseline designs in July. The prequalified contractor teams will bid using the plans that include their confidential concepts, a method that is expected to reduce cost, increase competition, incorporate the most current technology and result in a superior product. The bridge portion of the project is expected to let in October, with work to begin in early 2010.
Because the alternative technical concept process has so effectively helped to meet project goals on the bridge itself, MoDOT, IDOT and HNTB are using this process as well for the Illinois- and Missouri-side approach structures, which HNTB also is designing. Eight contractors already have expressed interest in working with the Mississippi River Bridge design team on these roadways.
Challenges stay big
Development of the Mississippi River Bridge has presented the project owners with a unique set of design and construction challenges. High waters and flooding are common in the unpredictable Mississippi River, for example, and HNTB and the four prequalified contractors are among only a handful of companies in the world with the expertise to design and build in these conditions. Potential also is high for a major earthquake in the area, and the entire length of the Illinois approach span must be built in deep alluvial soils, which, in an earthquake, are unstable and potentially subject to lateral spreading and widespread liquefaction.
Without precise engineering and design, if a major temblor were to occur, the ground would tend to flow downhill toward the river, rendering it incapable of supporting a load of any kind. Consequently, HNTB is carefully evaluating the possible ground motion and the soil structure to determine the potential width and depth of liquefaction in an earthquake and is designing the structure to withstand those forces.
The Illinois approach span faces an additional challenge. Twenty-four hundred feet of the 6,327-ft approach span crosses above land owned by four railroad companies and crisscrossed by 22 tracks. Thus, the bridge span must be designed and built to allow capacity for the railroad companies to expand in the future, and when the bridge is being built, construction must occur over the railroad land without hindering rail traffic. To prevent interference with current and future railroad business, IDOT, MoDOT and HNTB opened conversations early with the railroad companies and have actively engaged railroad officials for more than a year in reviewing and providing input on plans.
Because the bridge also must accommodate Coast Guard requirements, the design incorporates a 60-ft vertical clearance over a 2% flood. Its 1,500-ft navigational span will make the Mississippi River Bridge the third-longest cable-stayed bridge in the U.S.
Mistakes would be intolerable on this fast-track project. Because communication is vital to preventing errors and remaining both on schedule and on budget, project leaders established an office in downtown St. Louis and staffed it with decision makers from MoDOT, IDOT, HNTB and FHWA, giving them immediate access to and responsiveness from others who also participate in the daily project management process. MoDOT serves as the lead agency on the Mississippi River Bridge project, but both DOTs have fully cooperated and coordinated with each other and have yielded as necessary to ensure that the project will be delivered on budget and within the promised time frame.
Informed Citizen
MoDOT and IDOT have sought public input on the Mississippi River Bridge since the project originated in the 1990s. With the shift to a phased project schedule in 2008, MoDOT established the Citizen Information Group (CIG), composed of elected officials, local representatives, business owners, community leaders and residents. CIG members participate quarterly in local meetings and minority community roundtables to communicate the project timetable, discuss anticipated traffic impacts, gain input on work-force diversification, explain the project’s on-the-job training goals and seek feedback on the plans. A similar group, the Illinois Community Outreach Network, operates on the Illinois side.
While not designed to be a signature span, the Mississippi River Bridge will be a beautiful structure, enhanced by 400-ft-tall delta-shaped towers and aesthetic lighting that will be funded by sources within the region. In addition to improving safety and mobility, the Mississippi River Bridge project will create jobs, including those for socially and economically disadvantaged individuals and businesses, and will open up a new corridor for development in the bi-state region.
When it is complete, the Mississippi River Bridge will serve not only as an economic development asset for the Missouri-Illinois region surrounding St. Louis, but also will become a vital link in the national transportation network.
About The Author: Hague, an associate vice president of HNTB Corp., led the design of the Mississippi River Bridge. He can be reached at 816/527-2207, e-mail: [email protected]. Horn is a project director with the Missouri Department of Transportation and is overseeing all f
