Pocket tracks and turnback tracks

 https://en.wikipedia.org/wiki/Pocket_track

https://homenewshere.com/daily_times_chronicle/news/reading/article_f1438766-e88f-11ef-af97-673d0d3e5f1f.html

https://en.wikipedia.org/wiki/Balloon_loop

https://en.wikipedia.org/wiki/Toronto_streetcar_system_loops#Current_loops