I have used railroad in past with good success but unfortunately with my current project it has been nothing else than a huge pain.
First with installing its dependencies then getting errors relating to being unable to load application environment, models etc.
All my attempts to patch the gem and look for a fix to get the ball rolling were of no use, untill I tried to look for options to generating erd of a rails project. And I finally stumbled upon on rails-erd gem.
Installing the gem went smoothly and as the Graphviz was already installed. Running the bundle exec erd , quite easily generated the erd. However, it generates a pdf file unlike railroad which generates png file. The file is generated in the application root folder instead of docs folder of the app, like railroad does. I guess printing pdf files would be better.
So in short if you are facing troubles with railroad then I would highly recommend using rails-erd gem and save yourself the trouble.
Find out more about rails-erd at: https://github.com/voormedia/rails-erd
