sentences:  SR 231 is not part of the National Highway System, a system of routes determined to be the most important for the nation's economy, mobility and defense.The roadway that would eventually become SR 231 was established in 1940 as SR 24 Spur along a short alignment from Downtown Davisboro to the intersection with SR 24 in the northern part of the city.In 1943, SR 24 Spur was redesignated as SR 231, and was extended to its current southern terminus.