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The graph actually shows a separate item for "traffic signal conditions", which implies that "streetlights" are in fact different than traffic signals. (Look at the middle/upper-right; it's kind of hard to see).

http://www.nyc.gov/html/dot/html/signs/strlite.shtml

I don't live in New York, but I imagine they'd assume that the call centre isn't 24-hour?

It's advertised as a 24-hour line.

But the people who complain about noise don't? That would be interesting too.