 In 2009, WVDOT calculated that as few as 45,000 vehicles traveled along the highway at the Virginia state line, and as many as 62,500 vehicles used the freeway between CR 15 and CR 13 in Martinsburg.As part of the Interstate Highway System, the entire route is listed on the National Highway System, a system of roads that are important to the nation's economy, defense, and mobility.I-81 roughly parallels the Great Indian Warpath, an old Indian trail which connected New York to the Carolina Piedmont via Virginia and West Virginia.