Most people, especially in NY, speak of it as “the Thruway,” not I-87, nor “New York Thruway,” “New York State Thruway,” etc. That points to using some form of the signage for entry indications and as the name of the route. Visitors from afar will, however, home in more on the Interstate number.
So how to apply that, to the freeway, and to its entrances?
FREEWAY
“I-87 / Thruway” or “I-87 / NY State Thruway” (the shield does not have the word “state,” but that is the official name, the shield just didn’t have room for it).
Arguments against:
LENGTH: Not a problem. The name on the roadway itself is (almost?) never used with instructions (TTS and on-screen), because every entrance is named “to I-87 / …” followed by a best continuation onto the highway. If there are a few exceptions, we can fix those. So the long name would only appear on the segment line.
SINGLE NAMING: We have a rule that concurrencies should use the primary name of the roadway at that point. While technically this is a concurrency, the entirety of the thruway has this concurrency. And even though we would be choosing the state name over the Interstate number, the state name is really the primary name. COUNTERPOINT: This also holds true of the New Jersey Turnpike, yet we name the turnpike I-95, not I-95. My answer to that is… the same arguments apply. We SHOULD call it I-95 / New Jersey Turnpike.
SHIELDING: Some editors really like shielding on the map. The shielding system is touchy, and the only way to guarantee a shield is to call it ONLY “I-87”. This is a weak argument, because we can try it and see if we get shielding. Further, even if we cant get shielding, a cute UI feature shouldn’t take precedence over usable naming. There is also a hack that would fix this.
ENTRY
For entry ramps, go with “to I-87 / Thruway” (short form). Definitely no need to use “NY” here. Some of these instructions can get very long, so dropping NY has advantages, with minimal disadvantages. There is no confusion introduced by leaving it out. Those who know what the Thruway is will correlate Thruway with the shield and the highway without squinting or thinking. Those who don’t know what it is will be OK with the I-87 included in the instruction, and are unlikely to read the small shield lettering anyway.
I can’t think of any arguments against, other than the (non-)confusion addressed above.