They call it Highway forty after Us 40, which was its pre interstate name. Personally never heard it called fardy, other than in jest but we do like to have local ways to pronounce things. Exhibit a: https://en.m.wikipedia.org/wiki/Missouri_French

I know it’s after US-40 but I like that it’s a local shibboleth like “Missouree” (St. Louis) vs “Missouruh” (rest of Missouri) and BreadCo vs Panera. We used to say the geographic dividers between those two pairs were identical.

I had one professor who was an unironic “fardy” speaker. I think it’s not common under 50 anymore. But I also haven’t been in town for a long time.