at the end of the French and Indian War in 1763, the road to Philadelphia already extended to Winchester
Source: Library of Congress, An accurate map of North America. Describing and distinguishing the British, Spanish and French dominions on this great continent; according to the definitive treaty concluded at Paris 10th Feby. 1763 (Emanuel Bowen, 1767)
The Scotch-Irish and Pennsylvania Dutch migrated from Philadelphia into the Shenandoah Valley, converting game trails and Indian paths into wagon roads good enough to carry their agricultural products back to Philadelphia. The colony of Virginia did not build roads for settlers to move south, up the valley - there was no Virginia Department of Transportation then. The immigrants themselves constructed their roads.
Once counties were established, the county courts assigned responsibility for maintaining certain stretches of roads to nearby landowners. Their tithables were required to work several days a year to keep roads in good repair. The House of Burgesses recognized that settlement in the Shenandoah Valley would require county governments to handle such local operations, and authorized the creation of two counties west of the Blue Ridge in 1738.
The settlement pattern from north to south is reflected in the dates those county courts first organized and started making official decisions. Frederick County began operating in 1743, and Augusta County was officially organized two years later.
Today, I-81 and the earlier Route 11 parallel the Blue Ridge and transect Virginia, northeast to southwest. However, the original settlers did not construct their roads south of the New River and go straight to Tennessee. Carving the Wilderness Road through Southwest Virginia and finally across Cumberland Gap came after construction of a path through the Piedmont of Virginia into North Carolina (now US 220).