According to Wikipedia's article on railroad diagrams one of the first appearances of it was in "Pascal User Manual" written by Niklaus Wirth in 1973. Hardly a

According to Wikipedia's article on railroad diagrams one of the first appearances of it was in "Pascal User Manual" written by Niklaus Wirth in 1973. Hardly a new idea. It's been used in academia for ages when first teaching regular expressions and Extended Backus–Naur form to students.