The calcium chloride solution is good down to like -40 degC before it freezes. Check out this chart:
In one of the previously cited threads, another similar chart was posted that showed the properties of the two forms of the intermediate-temperature crystals that form upon cooling. As long as there is some solid salt in the solution, it is saturated, and will closely follow the chart. On highways and roads, it is a better de-icer than rock salt.