1. Riding in temperatures at or near 20-degrees isn't fun. But it doesn't appear to be actively hazardous, either.
At that temperature, the lube on my bike chain froze up, making my pedals stiff and making it hard to shift. Moreover, even with a full facemask, breathing air that cold was almost painful. Going up hills was harder than normal because I couldn't get my bike into first gear, and that meant my lungs were working like a bellows. That brought my core body temperature down, which sucked even more. It took me hours to warm up after I got into the office this morning, and my feet were so cold they hurt for the last five minutes of the ride. Plus, every time I stopped for a traffic light, I started shivering. None if that was at all good.
In retrospect, I needed a warmer hat and much warmer socks and shoes.
This afternoon's ride was much, much better, even though the temperature was only a half dozen degrees higher. Because let's face it, there is a world of difference between 13-degrees and 20.
I think from now on, I'm gonna have to reconsider commute riding under, say, 18-degrees. I like riding, but risking my health is foolish, even to avoid the New York City subway system.