The author of "The Silk Road" includes the supporting detail that the trade route is still widely used today to support the central idea of the selection. This detail helps emphasize the enduring significance and relevance of the Silk Road in facilitating trade and cultural exchange across regions over time. By highlighting that the trade route continues to be utilized, the author underscores its historical importance and the lasting impact it has had on global interactions. This supporting detail reinforces the central idea that the Silk Road has played a crucial role in connecting diverse civilizations and fostering economic activities throughout history.