Riley County and the City of Manhattan contracted BG Consultants to design a replacement for the existing bridge on South Manhattan Avenue and realign the adjacent Linear Trail. Two major design criteria were lessening the frequency of road closures in time of heavy precipitation and lessening the amount of debris collected in the stream, which contributed to heavy flooding.
The existing four-span concrete girder bridge was replaced with a 90’ – 106’ - 62’ prestressed concrete beam bridge. To reduce the frequency of road closures, the grade of the new structure was raised. Due to heavy traffic on this bridge, it was unable to close during construction. Therefore, it was designed to be built one half at a time. Temporary traffic signals were used to allow for one lane of traffic throughout construction. Since prestressed concrete beams were used, the center span of the bridge was large enough to span the creek without a pier in the center of the waterway. This removed one obstruction that had previously contributed to debris collection. The K4+3 prestressed concrete beams were made continuous by the composite concrete deck.
BG designed the bridge with a 6-foot pedestrian walkway to carry the Linear Trail across the creek. The trail continued under the bridge along the south berm to rejoin the existing trail. The former pedestrian bridge was removed, eliminating another debris-collector from the waterway.