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WILLETT, HOFMANN & ASSOCIATES, INC.
Consulting Engineers
Land Surveying - Transportation - Structural - Environmental - Architecture

 

 

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Savanna Bike Trail

Savanna, Illinois

 

 

The City of Savanna began discussions with the Illinois Department of Natural Resources in the late 1980s regarding the possibility of constructing a shared use path to become part of The Great River Trail and The Grand Illinois Trail, a system of smaller trails beginning in the Quad Cities and extending north along the Mississippi River to Galena, Illinois.  By the end of 1992 a preliminary path alignment was determined and federal enhancement (ISTEA) funds covering 80% of the design and construction of the path were approved.  Willett, Hofmann & Associates, Inc. was hired in 1993 to begin design of the path.

 

The desired path was to follow an abandoned railroad embankment into downtown Savanna. The path would pass through an endangered species habitat and a protected wetlands area, and border the U.S. Fish and Wildlife Spring Lake Facility, the Mississippi River and a public marina.  Bridges would be required so the path could cross the Plum River and two railroad lines. 

 

WHA investigated and designed a wide range of options for path alignment, and a number of design obstacles were overcome along the way.  The most significant challenge involved the railroad’s change of ownership.  Progress was stopped until the purchase was finalized, and then WHA repeated the review process with the new representatives.  The new railroad owners rejected a proposed crossing, but indicated that they would be open to the use of an overpass structure or a culvert constructed under their tracks.  WHA  investigated four alternate alignments, then narrowed it down to the final route that exists today. 

 

Another obstacle that had to be overcome arose from the fact that there was no economically feasible way for drilling equipment to access the area between the south abutment of the Plum River and the north side of the I&M crossing during the design phase.  Reasonable access was blocked by the two rivers, the railroad tracks, and the wetlands.  WHA and the geotechnical consultant agreed that it would be in  the  best  interest  to  postpone  making  borings  in  that  area  until  the  construction phase.  The pile foundations in the inaccessible areas were tentatively designed based on interpolation of obtainable information, and borings were done at the time of construction.  Time was allowed for the design team to review the boring data and, if necessary, make revisions to the final design.

 

The structures for both bridges were prefabricated steel trusses on pile-supported cast-in-place concrete piers and abutments.  Both structures were fabricated using corten (weathering) steel to provide a rustic look and eliminate future painting of the structures.  The structure over the Plum River is a 220 foot single span bowstring truss.  The structure over the tracks is 1,135 feet long and consists of fourteen spans at 71 feet with a center span of 141 feet.  The 71 foot spans are portal trusses and the center span is a portal truss with architectural arches added to resemble a bowstring truss.

 

The Plum River bridge was designed as a single span to match the abutment locations of a former bridge that had been removed in the early 1980’s.  The single span eliminated the need for construction of piers in the water, providing the greatest hydraulic capacity and the most aesthetically pleasing structure.

 

The length of the railroad overpass structure was governed by the railroad’s requirement of a 23 foot minimum vertical clearance over the tracks and the ADA requirement of a maximum grade of 5%.  The span lengths were determined based on the maximum length that could be shipped by pre-fabricated bridge manufacturers and were set on the piers directly from the truck, thereby minimizing the field labor required to erect the bridges.  The center span was set at 141 feet to exceed railroad horizontal clearance requirements and to provide a pleasant aesthetic break in the profile of the structure.

 

The necessary structure length was beneficial from an environmental standpoint, because the designated wetlands extended approximately 500 feet south of the tracks and were in the path alignment.  With the south half of the structure spanning more than 500 feet, impacts to the wetland area were only temporary during construction of the bridge and no mitigation was required. 

 

During the winter of 2000 / 2001, project engineers completed the final design of the path and bridges and prepared right-of way documents for required easements from the U.S. Fish and Wildlife Service, Savanna Park District, I&M Rail Link and BNSF Railroad.

 

The close monitoring of the costs allowed for early recognition of items that would cause cost overruns, but also allowed the tracking of items that would come in under budget, offsetting those overruns.  The final result was a project bid at $2.16 million dollars being completed on time for a total of $2.18 million, a cost overrun of approximately 1%.

 

The completed project is a beautiful multi-use recreation path with scenic overlooks, ties to the wildlife refuge and two landmark bridges.  In 2004 this project won a Merit Award in the Engineering Excellence Awards Competition by the Consulting Engineers Council of Illinois.  We are proud of this project and the benefits it has brought to the City of Savanna.

 

 

 

Scope of Work

· Topographic Survey

· Feasibility Study

· Development of Multiple Path Alignments

· Right-of-Way Documents

· Assistance in Procuring Right-of-Way

· Permitting from Local, State, Federal and Private Entities

· Coordination of Environmental Issues

· Plans, Specifications, and Contracts

· Coordination on Funding Issues

· Cost Estimate

· Construction Staking

· Grant Application Assistance

· Construction Engineering

 

 

 

 

Last Updated:  02/13/2009
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