State Route 166 is a primary state highway in the U.S. state of Virginia. The state highway runs 15.47 miles (24.90 km) from U.S. Route 17 in Chesapeake north to US 60 in Virginia Beach.

U.S. Route 17 (US 17) is a part of the United States Numbered Highway System that runs from Punta Gorda, Florida, to Winchester, Virginia. In Virginia, the U.S. Highway runs 255.83 miles (411.72 km) from the North Carolina state line in Chesapeake north to its northern terminus at US 11, US 50, and US 522 in Winchester. US 17 is a major highway in the eastern half of Virginia. The U.S. Highway connects the Albemarle Region of North Carolina with the Hampton Roads metropolitan area. Within the urban area, US 17 passes through the South Hampton Roads cities of Chesapeake, Portsmouth, and Suffolk and the Virginia Peninsula city of Newport News. Between Yorktown and Fredericksburg, the U.S. Highway serves as the primary highway of the Middle Peninsula. At Fredericksburg, US 17 leaves the Atlantic Plain; the highway passes through the Piedmont town of Warrenton and crosses the Blue Ridge Mountains on its way to Winchester in the Shenandoah Valley. The route from Tappahannock to Winchester roughly follows the Confederate march during the Civil War to Gettysburg.