There's a really good reason there isn't an OTF blessed by FHWA. If they put together an OTF themselves, it would deprive all of the type foundries of being able to sell their implementations of the FHWA Series fonts. I don't think that's a really important concern myself, but if I was FHWA I sure wouldn't want to deal with all the whiny capitalists bitching about it.
I don't think that's really a problem, not when so many
flavors of "Highway Gothic" vary noticeably both in terms of glyph design and metrics.
And if they blessed a specific foundry's existing implementation of the fonts, that would open them up to profiteering by raising the price to astronomical levels, the same way Meeker and Associates did with Clearview.
They have other alternatives. There is a pretty big market in open source typefaces. If I was calling the shots at the FHWA I would try partnering up with Google to modernize the Series Gothic typeface to make it more properly functional. Google is already well known for its Maps, Earth and Street View applications. Google also does a great deal of work on typefaces. Google Fonts is the biggest outlet of open source variable fonts. It only seems natural to me that Google could be a potential good partner on such an effort. FWIW, Google does have a typeface called "Overpass" that seems like an imitation of Highway Gothic or Interstate. It even has a variable weight axis. It's not a substitute for Series Gothic though. Still, it's interesting they do have such a typeface in their collection already.
You know as well as I do you can have an font that has literally every feature the OTF specification supports crammed into it and some shit-for-brains mouse jockey will stretch it out.
That's no justification for keeping a typeface primitive. If the FHWA is going to mandate features such as cardinal directions being in all caps, but with a larger first letter, then the fonts being used need a real native small caps character set. Faked small capitals look unprofessional as hell.
The rules against diacritical marks are outdated and arguably hypocritical. A lowercase "i" or "j" has a dot above the main stroke. Those dots shouldn't have any higher ranking than other accent marks like a grave, acute, tilde, diaresis, etc. 40 years ago when button copy signs were still common the letters had to be positioned on the sign panel one by one. Back then banning diacritical marks from lettering would have made sense. Now all the graphics are getting cut by vinyl plotters or the entire sign face is getting printed in one sweeping pass. The process is far easier and faster now.
Letter spacing for highway typefaces is deliberately loose, so there isn't any need for ligatures such as "fl," "ffl" etc. Likewise there's little need for a bunch of alternate glyphs such as a letter "a" with both double-story and single-story versions.
Variable fonts that have weight and width axes can more gracefully overcome space limitations on a sign blank without the lettering looking stupid as all hell. But, yeah, the mouse jockey actually has to turn on his brain to actually use those features.