We were hired as the prime consultant to provide engineering design services for the widening and reconstruction of approximately 5 miles of both southbound and northbound lanes of Tri-State Tollway (I-94) from IL 60 to IL 137, which included two interchanges at IL 176 and IL 137 and the Lake Forest Oasis on-ramps.

The Tri-State Tollway was widened from a three-lane cross section to a four-lane cross section in each direction, and the interchanges at the Lake Forest Oasis and IL 137 were modified to accommodate the additional lane. In addition, roadway lighting was added to the mainline and interchanges along the corridor.

Significant structure design was completed as a part of this project. On each of the dual three-span, PPC I-beam structures over the EJ&E Railway, design elements included a completely new superstructure using PPC I-beams to widen the bridge to the outside from a three- to a four-lane section, and substructure repairs and widening.

A three-span PPC I-beam bridge deck replacement carrying I-94 over the Metra Railway was also designed. The bridge was widened to accommodate a fourth lane in both directions of the interstate, requiring a partially new superstructure, and shallower beams were used in the widened portion to avoid decreasing the low beam elevation. Work also included construction of two retaining walls on the IL 176 entrance and exit ramps using performance-based special provisions, and approximately 4,000 linear feet of noise abatement wall north of IL 176.

The project also included complete replacement of the IL 176 interchange, including a new bridge structure. At this particular bridge location, the vertical profile of I-94 was lowered 6 feet to improve the interchange. Additionally, the horizontal alignment was modified slightly to address current superelevation criteria. The new bridge consists of a 215-foot, three-span PPC I-beam structure supported on column bent piers and semi-integral abutments. The new bridge can accommodate future expansion of IL 176 and a realigned bike path. With the existing structure accommodating an overall length of nearly 300 feet with five spans, extensive fill supported by retaining wall was necessary.

To minimize disruption to traffic, a counter-flow lane was implemented during construction. With the significant change in profile, detailed staging plans with design of a temporary support system were included. Because a 48-inch water main was in close proximity to an abutment, special provisions were developed to describe specific performance requirements during construction. Our firm was given an “A–Exceeds Expectations” for our consultant evaluation for the project, in part because of our ability to be responsive in meeting the needs of the Tollway.

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