Why are there different fonts on highway signs?

(WHTM) — Now that you know why highway signs are green, it's time to dive into another highway sign question: why are some signs in one font and other signs in another?Before that question is answered, let's talk about the history of highway sign fonts.
The main typeface seen on signs for many decades is called "Highway Gothic." This typeface is defined by the Federal Highway Administration (FHWA) Standards Alphabets for Traffic-Control Devices, which was published in 1948.These Atlanta tr