We usually have very cold mornings from November to March around here. We occasionally have a 30 something degree morning with safe roads, so I can sometimes go outside, but I use my treadmill many days.
About the dark, you can get lights and reflective vests so that you can be seen by drivers. A teen I know was hit by a car when she crossed the road on a run to return home. A neighbor of mine expressed how alarming it is for her to come upon me suddenly running in our circle in the dark, even though I get off the road when the rare car comes by. So, over the years, I've learned to be safe! Now I have a reflective vest I can put over everything. I have a clip on light that goes right on my front. My favorite item is my wind-breaker cycling jacket I bought when I was training for a 100 mile bike ride. It is awesome quality for weather protection and it is totally BRIGHT Yellow/greenish! That was totally worth the high-price I thought I was paying at the time. I've also just purchased a white running cap. I've also carried a flash light... awkward, but potentially life-saving.
I've been comfortable going outside down to 22 degrees. I have a tech l/s shirt to layer under the jacket and lined work-out pants that do a nice job. Mittens and head covering are essential.
I usually check the weather, moan, and if I do push myself to get out there, I am usually always invigorated and proud of my fortitude! I only regret it when there are high winds.
Today I thought about doing some weight training! At least my brain got exercise. : )