 The only portion of SR 51 that is part of the National Highway System, a system of routes determined to be the most important for the nation's economy, mobility, and defense, is the entire length of the SR 17 concurrency from Canon to Bowersville.The roadway that would eventually become SR 51 was established at least as early as 1919 as part of SR 17 from Carnesville to Canon.By the end of 1921, SR 17 was shifted eastward.