To cite opentripplanner package in publications use:

  Morgan et al., (2019). OpenTripPlanner for R. Journal of Open Source
  Software, 4(44), 1926, https://doi.org/10.21105/joss.01926

A BibTeX entry for LaTeX users is

  @Article{,
    title = {OpenTripPlanner for R},
    author = {{Malcolm Morgan} and {Marcus Young} and {Robin Lovelace} and {Layik Hama}},
    journal = {Journal of Open Source Software},
    year = {2019},
    volume = {4},
    number = {44},
    pages = {1926},
    doi = {10.21105/joss.01926},
  }