Great article.  Kudos to them

https://www.fox13now.com/news/local-news/slc-converting-16-000-street-lights-to-make-them-energy-efficient-dark-sky-friendly

This sucks, but hopefully they'll use Signify RoadFocus RFL's i like the design of those.
Also, i think Salt Lake City, Utah has already been LED for a few years now. They could just remove the refractors on the remaining HID's?

They started upgrading a few years ago but my guess is that they still have a long ways to go.  Some of the cities around here will upgrade fixtures when the HPS bulbs in them burn out.  I highly doubt they'll be reusing any of the old traditional fixtures and will instead be doing a complete upgrade including fixture in order to get the best light output pattern that they can.  Those RoadFocus are the way to go.  We have them here when they were installed starting in 2017 and save for some underground wiring issues, which are common here, i'd say about 98% of them are still going strong. They installed 4000K and many of them now have a slight greenish hue to them, so sort of a color shift.  Kind of looks like a MV/MH hybrid.  But they light up the roadway much better than the old HPS cobraheads. 

Interesting, we also have still Hadco RX1's and RX2's on our interchanges, some white, black or gray. Most of them that i've seen are now dying or dead and are being replaced with white or black or gray Lumec RoadFocus large fixtures. the ones that are failing one by one where i live are flashing (one at least) and the rest are out or missing half the diodes. Those recently got replaced by white Roadfocuses. The RX fixtures where installed around 2013 when they reconstructed an interchange here and worked very well until recently.

If they are flashing, it's a good chance that it's either the driver, or the full power isn't being delivered to the pole.  The Phillips RoadFocus that were installed here (they were still Phillips back then) will flash/flicker when there is an issue with a lack of power being delivered.  we get that a lot due to the underground power line issues that arise due to shifting soil. 
Some of the naysayers to LED were quick to point out that the LED installations are failing already but the electrical company was quick to point out how the fixtures worked great when the power delivery issues were resolved, no issues were found with the fixtures or drivers.  Most of the modern LED fixtures run multi-volt drivers, meaning they can run on anything from anywhere from 120-240 volts but if they drop below 120 volt they get temperamental. 

Interesting, I might try this on my RFS to see if it flashes when it receives low voltage. I have a NYC 150w HPS OVZ and it has a red low voltage warning light that lights up at around 90v. The ballast (electronic HPS) also starts to get temperamental at that point too.

In theory one could probably fit one of those low voltage warning devices to a LED luminaire too but they seem to have gotten limited adoption. NYC was the only municipality that specified them to my knowledge. I suppose the modern wireless node controls might be able to relay a low voltage or luminaire out condition back to the utility though which eliminates the need for such a device.