Hamilton County – County Route D-46 Bridge Over the Boone River

The existing bridge was a 186’ x 14’ pin- connected camelback high truss listed on the National Register of Historic Places.  The rugged terrain adjacent to the Boone River resulted in steep roadway approach grades and sharp horizontal curves to navigate motorists down to the Boone River floodplain.  The existing roadway alignment fell well below current design criteria and created hazards for the traveling public.  Based on the topography and the desire to avoid the existing historic bridge, it was clear that the new bridge would need to be constructed on an alternate alignment.

Several alternate alignments were considered prior to selecting the location.  The final selected alternate consisted of a 454′-0 x 32′-0 pretensioned prestressed concrete beam bridge and nearly a mile of grading.  Grading through the rugged terrain resulted in fill depths of over 45 feet and cut depths in excess of 35 feet.  Despite the extensive grading the bridge still soars over 70 feet above the Boone River.  CB&A assisted the County from concept to preliminary and final designs.  The project required extensive coordination with the client and sub-consultants to face the challenges of this complex site.