Alan Brown's History of America's Speedways documents more than 8000 race tracks in the US and Canada, of which fewer than 2000 are still in operation.
The Ghost Tracks on OpenHistoricalMap project is an effort to document the locations of old Racing venues. The NA Motorsports website provides a way to view the data collected and added to OpenHistoricalMap. The race track data in OpenHistoricalMap is licensed under a CC0 license which is equivalent to the concept of public domain.
A YouTube channel has been created to present deeper dives into tracks. Current overviews are of Thompson Speedway and Watkins Glen. Other videos are under development.