There's some that are purely due to space constraints, favourite pet-peeve example is a highway with an overpass crossing it.

In the rural case, the offramp will branch off first and the on ramp will be after the overpass and the drivers taking each never meet.

In the space constrained case, theres one extra lane that serves both, where the drivers taking the on-ramp cross paths with those taking the off ramp. This configuration is absolutely cursed!