In that sense I see “am going” as present continuous tense of the verb GO, describing what you are doing on the train right now, not as an auxiliary modifier that places the verb “to work” in the future, because “to” in your example is a preposition and “work” is a noun.
Similar to “I’m travelling to work”.
Ah, I see, I misread. However, I think you did too - licheam was using it as going to + noun, not going to + verb. You’re right that going to is a present continuous form of the verb go - I don’t think anyone’s disputed that.
“I am going to + verb” is for the future, but “I am going to + noun” can be future or present. Hence the ambiguity in the examples Heracles gave, an ambiguity which “I am going to go + verb” solves.
I am going to work this afternoon. However, I am not going to go to work because I work from home.
'Cause you know sometimes words have two meanings.
Yeah. Sorry I meant “work” the place, not “work” the activity. Replacing with something that is only ever a noun.
I am going to the Chrysler Building. <— progressive present.
I am going to go to the Chrysler Building. <— composite future tense.
I am going to the Chrysler Building tomorrow. <— future implied by context.