From A Wiki of Ice and Fire
The Kingsroad is the main overland route in the Seven Kingdoms, it extends for almost two thousand miles, from the northernmost end at Castle Black, at the Wall, it runs south to the capital, King's Landing and continues on through the Stormlands to Storm's End. However it is nothing like the great Valyrian roads of past.
The Kingsroad was built during the reign of King Jaehaerys the Conciliator, about 200 years ago. Its quality varies from place to place, its main section is between King's Landing and the Neck and sustains numerous inns and villages along its length. To pass through the Neck it becomes a causeway. North of the Neck and south of King's Landing the road winds down. Inns exist, but they are farther apart and much less able to accommodate large parties.
Once the Kingsroad moves beyond Winterfell, the grand road becomes a sparsely travelled path, and aside from a few farms, there’s little around, until it reaches the Wall. Similarly, once the the Kingsroad moves beyond King's landing, the grand road becomes little more than two narrow dirt tracks, winding back and forth on itself.  But over all it increases mobility and speeds of travel.
The Kingsroad crosses the High Road at the Crossroads Inn, forks at King's Landing leading to Casterly Rock and forks little south it leading to Highgarden by way of the Roseroad. The Kingsroad enters King's Landing from the north through Dragon Gate . It starts up again across Blackwater Rush to Storm's End.