Why progress is slowing around the UN's Sustainable Development Goals

It's United Nations General Assembly (UNGA) week, when heads of state and representatives from at least 145 countries descend upon Manhattan for the global body's annual high-level session. For New Yorkers who aren't participating in or covering the sessions — like my Vox colleagues Jonathan Guyer and Jen Kirby are, dashing from meeting to meeting — UNGA week means one thing: gridlock alerts, when the combination of crowds and security closures turns the east side of Manhattan into a parking lot. Cars aren't the only thing stuck in traffic at the United Nations, however. One of the main topics of…