If it's in bumper to bumper traffic, it will barely be using any energy, so it would give an increase in efficiency.

Cold weather negatively affects range, but that effect will be less significant than with an EV car, since some of the factors such as interior heating and winter tires play a much smaller part in energy usage on a Semi. The cabin may be a little larger than a car, but not substantially so the amount of heat needed will be similar. Semis don't switch tires in the winter.