i hear the winter is actually mild in December in Iceland. I am thinking of going at this time. Has anyone done a road trip in the winter and are the roads safe for travel?
I'd never do it. Driving there in summer is already complicated, let's imagine in winter, with most of the roads covered with ice. Distances are huge in Iceland and winter conditions make them double up. If you add to this the light problem, I guess that doesn't sound like a great idea...
The wintertime climate in Iceland is milder than that of northern Europe, Canada or the northeastern and Midwestern USA, but the problem is darkness - plenty of darkness. In December, the sun doesn't rise until around 11:00am and sets at 3:00pm. That means your window to drive during daylight hours is very narrow. So it depends on how comfortable you are driving at night.
Icelandic roads are safe and well-maintained, and mobile phone coverage is very good, even in desolate areas, so if you break down or have a problem you can count on assistance arriving before too long. The biggest potential hazards are free-range livestock crossing roads, which aren't easy to see at night, and black ice. There's a good reason why the speed limit is no more than 80km/h (49mph). However, Icelandic drivers are very safe and almost always follow road rules.
In Reykjavik, outside the city centre roundabouts (traffic circles) are more common than traffic lights, so make sure you know how to drive through a roundabout and are comfortable with it. Although Reykjavik has only 150,000 people, there are a lot of cars and there are definite morning and evening rush hours, so traffic can be a bit of an annoyance.