Pigtail Auto Loops

Routes can curve so completely that sometimes they loop all the way around and cross over themselves at a different elevation. Generally this happens in mountainous areas or in tightly-confined urban areas where there isn’t enough space to create a reasonable grade with a straightaway. This simple but dizzying solution goes by several names including spiral, loop and pigtail. I’m partial to pigtail simply for its whimsical imagery, of paths coiling and curving in concert with rolling contours, of roads behaving in magical ways as they wind their way through tough terrain. Railway pigtails can be found throughout…

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