Porter-Simmons Roundabout

City of O'Fallon, Illinois


On the heels of constructing its first roundabout project at State and Obernuefemann, the City of O’Fallon once again selected Horner & Shifrin to assist in obtaining a Congestion, Mitigation, and Air Quality (CMAQ) grant, planning, and designing their second roundabout at the intersection of Porter Road and Simmons Road.

Located just north of the new 200-acre Family Sports Park, Horner & Shifrin integrated the shared-use path into the roundabout design to facilitate the connection of the park to the roadway system. The project was constructed using a road closure of approximately 30 days and open to traffic before the start of the school year.

Initially Horner & Shifrin prepared, and was successful in obtaining, CMAQ funds for the construction of the roundabout, requiring only a 20% match by the City of O’Fallon. To justify the roundabout, Horner & Shifrin showed that constructing a roundabout at the intersection would reduce delay, especially with the construction of a new high school to the northwest of the roundabout. The traffic added by this new school and well as new residential construction near the roundabout was causing significant delays with queues in excess of 20 cars during the peak period in the morning and afternoon school commute.

The roundabout was designed using actual traffic counts obtained by Horner & Shifrin and traffic projections based upon the new school and residential construction. A shared-use path encircling the park was integrated into the roundabout design.

Horner & Shifrin was able to coordinate the utility relocation such that all of the utilities were moved before the project was sent out for bids. Since it is difficult to construct a roundabout while maintaining traffic, especially trucks and agricultural equipment, Horner & Shifrin employed a creative strategy by preparing special provisions to allow the contractor to close the road for 28 calendar days. It was critical to both limit the amount of closure since the adverse travel was excessive as well as completing the roundabout before local schools were back in session, which it was, approximately three weeks before the start of the school year.

This project was a 2012 Engineering Excellence Merit Award winner.





O'Fallon, Illinois

Year Completed


Innovation. Agility.
Reliability. Horner & Shifrin.