Well, the answer will depend on what it means exactly to be "impaired" - I assume here that the question means "under the influence of alcohol".
Some studies have found an influence of alcohol consumption on reaction time, but it was more around 10% than 50 % -then the answer is "false". However, I can imagine than in some cases, for example when the reaction has to happen very fast or is difficult, it could be twice as slow. This is rather rare, and i would say that "double" is too much - false.