I tell people the purpose of graphic design is to communicate a message other than the art itself. The best illustration is comparing design to music with lyrics. The message is the text in the lyrics. Graphic design is the music that carries, illuminates, and interprets the massage.
Sometimes, the necessity of communicating the message with as much clarity as possible overwhelms all other concerns. Such is the case with highway and traffic signs.
A large amount of study and testing goes into the effort to identify the best sign font when the viewer has only a split second to see, read and process a critical message. It is no exaggeration that lives are at stake when the traffic is heavy and the speeds are high.
The attached video produced by media provider, Vox, reveals the latest. https://youtu.be/eky17clTEeQ