The roads and sidewalks are usually not too bad during the winter, unless there is a significant amount of snow or more than a little ice. It depends on how harsh the winter is, but I would say that the roads are okay about 70-80% of the days during the winter. It also depends on exactly where you live, as more densely populated areas are obviously going to be better cleared. Ice is also a problem. Ice is common and requires that you find an ice free surface, or run with caution. You will not be able to run as fast if it is snowy or icy, so if you want to run fast, you need to either wait until better weather or get a gym membership at one of the nearby colleges that has an indoor track.
I ran indoor track three years in high school, and we were usually able to get in a good amount of running. Only in January and February would we have many days where we had to stay inside, and this was usually more due to cold temps than snow. As long as you are resourceful in finding ways to get your running in, and can handle running in the cold, you should be fine.