To cite r5r in publications use:

  Pereira, R. H. M., Saraiva, M., Herszenhut, D., Braga, C. K. V., &
  Conway, M. W. (2021). r5r: Rapid Realistic Routing on Multimodal
  Transport Networks with R5 in R. Findings, 21262.
  https://doi.org/10.32866/001c.21262

A BibTeX entry for LaTeX users is

  @Article{,
    title = {r5r: Rapid Realistic Routing on Multimodal Transport Networks with R5 in R},
    author = {Rafael H. M. Pereira and Marcus Saraiva and Daniel Herszenhut and Carlos Kaue Vieira Braga and Matthew Wigginton Conway},
    journal = {Findings},
    year = {2021},
    doi = {10.32866/001c.21262},
    url = {https://doi.org/10.32866/001c.21262},
  }