Transportation officials say an $18 million reconstruction of Spearfish's main Interstate 90 exit could take up to 20 months to complete.
Construction on the Exit 14 interchange is slated to begin in 2015. Officials revealed their preliminary design this week.
Engineering Supervisor Karen Olson says the design is a result of meetings held when the project was initiated in 2009.
Officials collected data on traffic volume and operations, finding that 66 accidents have occurred at the exit in the last four years. The study found insufficient distance between each signalized ramp intersection and no safe pedestrian connections.
Changes include lowering I-90 by 3 feet to improve sight distance, adding more 27th Street lanes and building a 10 foot wide pedestrian and bike path.