The phrase "dust tracks on a road" refers to Zora Neale Hurston's desire to travel and wander away from home.
In chapter 3, "I Get Born," Hurston explains that she didn't take to walking as quickly as some other babies do. Her parents worried about the fact that she would crawl but didn't walk. One night, her mother gave her a piece of cornbread and a sow came into the kitchen—likely looking to have a bite for herself. In response, Hurston pulled herself upright, clinging to a kitchen chair. She started using it to walk around the chair and away from the sow.
She says that once she could walk, the urge to wander set in. She always wanted to go, to explore, to walk into the doors. Her mother worried about her safety. She said that an enemy of hers probably sprinkled "travel dust" on the doorway when Zora was born and that's why Zora wanted to wander so badly.
The phrase "dust tracks on a road" comes from this desire and from the journey that all people take. The book is about Hurston's life—the tracks she's left behind her as she wandered. Those are the steps that have helped make her into the woman she is. It's her history, written in the road she wandered down.