Some pending sources:
https://www.nps.gov/subjects/transportation/upload/NPS-Active-Transportation-Guidebook_2nd-Edition_July-2023_low-res.pdf
https://www.nps.gov/subjects/nationaltrailssystem/upload/National-Trails-System-Act-Amended-2019.pdf
https://sgp.fas.org/crs/misc/R43868.pdf