ELI5 Right and Left Hand Traffic - which is more popular?

Which is more popular, driving on the left side of the road or the right? How has this changed in the last 100 years? How did Sweden manage to make the switch from left hand traffic to right hand traffic in one day? What are the practical considerations? Is this the same for rail and boat transport? ... we explain like I'm five Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: cincy2000, rappatic and definitely_robots To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Join us on Twitter: https://www.twitter.com/eli5ThePodcast/ or send us an e-mail: [email protected]