Once it gets below freezing, I'll usually opt to drive. Every now and then I'll ride, or at least flex my schedule so I start once the sun has started warming things up and by the time I am halfway to work it will be in the mid 30s. I don't want to ride in the dark in sub freezing temps though. All it takes is not seeing an icy patch from someone who left their sprinkler system on to get some bumps and bruises.