we should always try to retreat - take a step or 2 back. don't escalate the situation.
people are frustrated at their own situations, their wife, kids, boss, dog, neighbors, their bald spot or horriblw waistline...
and they'll take it all out on someone who angers them in traffic.
Make it a point to take a step back. try to have witnesses/camera showing he was CLEARLY the aggressor and you did NOT want this fight. if you do protect yourself, it's last resort. Way too many situations are 2 angry dudes running at each other. No matter who throws first punch, they both started it, and whoever is left live will probably go to prison.
People should just stop and think for a moment when that anger kicks in. Think about the consequences. Think about what you're really mad at, and change that instead. If you're exhausted from an awesome workout and evening sex with your hot girlfriend, you're not going to have that internal rage to jump out of car and start throwing haymakers at an old person. you're too happy and content in your situation.