When running rails side by side. Minecarts seem to like to run together because of their hitboxes. However, in a recent furnace array, I built I put Hopper Minecarts next to each other and had a stopping point for them when turned off. I noticed that the south side would stop. But that north side wouldn't. I did some testing and concluded that even on unpowered rails when two minecarts are side by side, they will travel slowly from north to south show in this video. https://youtu.be/5Bs4uVAdEI0