Might I suggest that your time behind the wheel is your chance to express the anger you feel the rest of the time? Isolated in our own world, often alone, we get the chance to behave badly, and it takes some self-awareness to keep a grip on things. Try listening to some favorutie (soothing) music, or maybe a talking book to occupy you, and distract you from the attitudes of other drivers. Otherwise, try and elminate what ever is making you angry in your day to day life, which obviously manifests itself when you are driving.