Strangely enough, Stoicism. I try to recognize what I can control and what I can't, and I try not to let things I can't control scare me into inaction.
Stressing about other drivers that you can't control? You're emotionally exhausted before you get to work. Stressing (within reason, perhaps better stated as "mentally focused on") about how to do X in project Y? Perfectly reasonable, that's a task you need to get done and that stress/focus keeps you on the ball (overdone can still leave you mentally/emotionally drained, or hyperfocused can leave you unable to think clearly about the task because you need to step back and view the whole picture).