AZ 238; posted 60 MPH?

[howlincoyote2k1]

I recently noticed that SR 238 in Arizona is something of a unicorn, in that it has a speed limit of 60 MPH. In all my driving all over the state of Arizona, I have not encountered another road in the state with a posted speed limit of 60 MPH and it has raised some questions about it for me.

Are there any other roads in Arizona posted at 60 that I just haven't seen?

Why is AZ 238 posted at 60, instead of the more conventional 55 or 65 commonly found elsewhere in the state?

If AZ 238 can be posted at 60, why aren't more roads posted at that limit?

This is something I find a bit confusing, but at the same time oddly intriguing. It's a total road-geek nitpick of sorts, but I guess that kind of thing is why we all visit this forum.

EDIT: GSV for reference It also looks like the speed limit was bumped from 55 to 60 sometime between 2015 and 2019 as well, according to GSV

[Max Rockatansky]

It was 55 MPH when I lived in Arizona.  Looks as though it was raised after 2015.