Road Rage a mental illness?

Intermittent explosive disorder involves multiple outbursts way out of proportion to the situation, often including threats or aggressive actions and property damage.The disorder typically first appears in adolescence - the study identified the average age of onset as 14.
What The? Given that the survey has been conducted in the US, I am not sure whether or not it really applies here in Australia. I mean for a start we don't carry shotguns in our cars and don't tend to kill people when they merge into us without indicating. Thats more an American tradition.
"It is news to a lot of people, even specialists in mental health services, that such a large proportion of the population has these clinically significant anger attacks" Prof Kessler said.
It news to me too buddy! Nevertheless, there WAS a survey of similar nature conducted by Proton Australia (yes odd source) to find out the statistics for Road Rage for young drivers (17-20):
60 percent of the 3000 respondents had at some stage in the past year either perpetrated or been witness to a road rage incident.Proton
It seems to me that Road Rage occurs when I have had a bad day and I've just about had it and then someone in a Toyota Landcruiser decides to cut me off. If getting angry and swearing at the driver is a Mental Illness, then please send me my disabled parking permit.
Update :
Spinopsys gives a view on the article