Way back in the days of old, carnival workers used to ask the next party in line if they wanted to split up and fill the last seats in one ride and then the next seats in the next. If they declined, the workers would hurriedly ask how big the next few party sizes were and if anyone wanted to fill the seats. This was inefficient, and put a lot of stress on the young, inexperienced, low paid worker to manage a line and a ride at the same time.
So, theme parks created single rider lines where families who WOULD be willing to split up if it meant they got to jump on the next ride vs waiting for it to go around again could self-identify so the ride operator no longer has to manage the line and the ride, but just the ride. When he counts out his groups seats, he just has to count the empties and grab those people from single rider.
That's it. That's what it's for. To make the employee's job easier and the ride more efficient. It's not about giving single travelers an advantage over families - that would not be profitable for theme parks (who want to attract more goers, not less, and every car with 5 is better than every car with 1). So, anyone can use it b/c anyone can fill the "efficient" role.
PS - When I was a teen on the Jersey boardwalk, my fam ROUTINELY volunteered to split so we could ride faster and then get in line again for our favorite rides...anything to make lines go and to get us more rides each night...
. Plus, financially, Disney appreciates big old families and groups rather than “singles”. 7,675 people can go through the single rider line if they want to. Single just means “one” ( with the understanding that you might/probably will be separated from your group.
