It is assumed that you don't (want to look as if you) know anyone there.
- 1 other person, not at an end: Sit on the end farthest from them. If they're in the center and have bags, sit on the side such that their bags are between you. If they don't have any, sit to their right if they're right-handed or you don't know their handedness. If they're left handed, sit on their left. If they're ambidextrous, sit so that they're on the side of your weak hand. If you're ambidextrous, too, sit so that they're on your left.
- 1 other person, on an end: Sit at the opposite end.
- 2 other people, neither at an end: If they're far apart, bisect the line segment between them. If they're not, follow the rules for 1 person, treating the two as one; if their handedness is different, treat them as an ambidextrous person.
- 2 other people, 1 is at an end: Sit at the other end unless this would put you closer to the non-end person than bisecting the segment between them. In that case, bisect.
- 2 other people, each at their own end: Bisect.
- 3 or more people: Bisect the space between the farthest-apart people.
note: this is a rather pathetic attempt to explain the way that people who are overly socially conscious will sit.
the reasoning behind sitting on a person's strong side: they can't get a swing with their strong arm; if they tried, it would hit the steps. it's more important that they can't get a swing than that you can, hence the decision tree.