Emotiv EPOC controlling a car, bending a spoon
Such a system could certainly work, but I could picture numerous other events that might produce a similar arousal reaction: a song on the radio, a sudden change in driving conditions, etc. In order to differentiate road rage from other kinds of arousal, it might be useful to look at some other measures as well: jaw tension, facial expression, etc. Also, I'm not sure shifting the car into neutral is a good road-rage countermeasure. Maybe putting on soothing music and dispensing a cup of chamomille tea would be more effective.
UPDATE: The same folks use the EPOC to do the proverbial "bending a spoon with your mind" trick: