Old IL Traffic Signals

[Super Mateo]

Questions for those of you in IL:

I was sent over to Orland Park, IL today to run an errand for my employer.  I took a short drive over there, and the intersection and signals at the intersection of 94th Avenue and 151st Street haven't changed or been updated at all.  It's the only intersection I've found in the area where the trusses (or is it mast arms?) still exist and the light on the far left has the red between the two bars.  In many locations, the truss/mast arm bars are still there, but the actual lights have been replaced and/or repositioned, like this.  A 12-8-8 signal appears southbound here, as well, which is now a no no.

So, my questions:
1.  When did these get phased out?  I know it was before 1990, as 171st and Harlem was replaced with monotubes, and all installations since have had the single tubes.
2.  Do any of these still survive elsewhere in the state that haven't been updated?
3.  Was there a specific reason these were all phased out?  I'm guessing that they cost a lot and it was hard to get more signals up on the bar.

[Revive 755]

2.  There are a lot of them still in Illinois - enough that any list would quickly get long.

3.  I guessing it was a combination of strength and length.  I do know agencies that have the trussed mast arms get a lot more careful with loading and will start asking for structural /loading calculations much sooner than they would for a modern monotube arm.

[Super Mateo]

Yeah, they do look like they would be a lot harder to work with than a basic monotube.