NDOT, Tryon-Mullen

Environmental Sciences

The Challenge: 
Nebraska Department of Transportation (NDOT) wanted to widen and resurface 13 miles of highway N-97 between Tryon and Mullen. Improvements to the road were critical, but the NDOT wanted a cost-effective solution that would safely function for the long-term without negatively impacting the nearby Dismal River.  

The Solution: 

Our Transportation team was hired to complete the project. With an eye on cost-saving strategies, our team provided preliminary and final design for curb and flume, storm sewer, retaining wall, guardrail removal and replacement, permanent widening, grading, and asphalt overlay. The approved strategy resulted in a 24-foot surfaced top and six-foot-wide earthen shoulders. 

Our Environmental team was tapped to complete documentation in accordance with the National Environmental Policy Act. To complete the project, we conducted a Section 4(f) initial assessment, biological evaluation, and prepared a Level 2 Categorical Exclusion for the Nebraska Department of Transportation.

Project Benefits: 
Our Transportation and Environmental Sciences teams worked with NDOT to design a retaining wall in order to avoid impacts to the Dismal River.  This design was challenging due to sandy soils, the need to minimize roadway closure, and to avoid impacting the Dismal River. We developed a custom braced sheet pile wall, and at 420’ long x 12’ tall, it mitigates environmental issues to the Dismal River nearly 50’ below the roadway surface. The project will preserve the transportation asset, improve the reliability of the transportation system, and perpetuate the mobility of the traveling public.