To cite package ‘ntdr’ in publications use:

  Kliems H (2024). _ntdr: Retrieve Data from the National Transit
  Database_. R package version 0.4.0,
  <https://CRAN.R-project.org/package=ntdr>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {ntdr: Retrieve Data from the National Transit Database},
    author = {Harald Kliems},
    year = {2024},
    note = {R package version 0.4.0},
    url = {https://CRAN.R-project.org/package=ntdr},
  }