SR 9 is the main east–west highway of northwestern Loudoun County, connecting Leesburg with Hillsboro and the West Virginia cities of Charles Town and Martinsburg. As a result, the state highway and its West Virginia continuation are a major, overburdened commuter route between the Eastern Panhandle of West Virginia and Washington, D.C.
SR 9 is the main east-west road in northwestern Loudoun County, linking Leesburg to Hillsboro and connecting to Charles Town and Martinsburg in West Virginia. Due to its heavy traffic, it serves as a major commuter route between the Eastern Panhandle of West Virginia and Washington D.C.