= why does 116 street on the 1 have a lack of pillars between the middle and south bound tracks? =

I don’t know for sure, but my best guess is because of the skylight is where the pillars would be and it’s reinforced differently to accommodate it. If you looked a little farther down there are pillars in between those tracks past the sky light

The pillars you are referring to are to support the passenger overpass and the original headhouse, which was demolished for being too unsafe for pedestrians

Two reasons:
First, the line goes directly into a concrete lined rock tunnel which doesn't require support columns

Second, the uptown track is located under the street which needed to support the roadbed and streetcar tracks directly above it. The downtown and bypass track is under the mall medium, which doesn't require the extra support

Does anyone know if deeper lines need pillars? The 1 is like that going uptown from what I remember seeing
Depends on how when & the material the tunnel