David Elson Gratz (July 7, 1927, in Columbus, Ohio – October 19, 2017) was a professional engineer best known for his work on, and notable for his extensive historical documentation of, the Monongahela Railway.
In 1957, he began work in the engineering department of the Pittsburgh and Lake Erie Railroad.
Later that year, he became Track Supervisor of the Maintenance of Way Department of the Monongahela Railway.
In 1974, Gratz was appointed Superintendent of the Monongahela Railway, a position that he held until 1989 when he became the Director of Real Estate and Labor Relations.
With access to over 11,000 glass plate and acetate negatives dating from the early 1900s, along with additional photographs by co-author Terry E. Arbogast, historic maps, timetables, and other documentations, Gratz produced the comprehensive 212-page book, published in 2003.