First, let me take this opportunity to deny that I had any part in creating this puzzle :)

In Chelsea's confirmation of glyph 6, she says she rode off on the L train... What happens if we follow her?

(Based on http://www.mta.nyc.ny.us/nyct/maps/submap.htm and http://www.mta.nyc.ny.us/nyct/service/lline.htm )

The intersections were found at the west end of the map, where the L stops at 8th ave (transfer to 8,C,E,M10,M14)- This is the stop referenced in the clue, so we'll start here. The L has 24 stops (including this one), of which 6 have train transfers and all but one have bus transfers. I can't find any patterns in these, perhaps someone else can. Other miscellaneous transfers are the PATH (New Jersey) trains at 6th, and the Long Island railroad at Atlantic ave).

Chelsea mentions the train's headlights, which may be important: The L is underground for only part of its route, once it gets to Brooklyn it goes aboveground. Unfortunately, I don't recall the exact point at which this occurs. :\ Miguel? ::poke poke::

What if the numbers in the glyph refer to stops? 10 and 14 are "taken", 80 and 66 are too large for this, which leaves 4, 15 twice, and 20. Stop 4 (counting from 8th ave) is 1st ave, nothing special there (buses: 9, 14,15). Stop 15 is is Wilson Ave and Moffatt St (buses: B20,B66). Stop 20 is Livonia Ave, the only stop without any transfers whatsoever.