"Boynton Bicycle Railway System. About the Long Island Boynton Bicycle R. R. in 1896. It rode on a single rail and was supported by an overhead guiding beam. In theory there could be coal and other freight cars, but the only actual photos show an 18 compartment electric passenger car made of bamboo and steel. A dual rail system could run bidirectional traffic. It was by nature very narrow.
https://www.gutenberg.org/ebooks/74783
https://www.gutenberg.org/ebooks/74783