Everybody I know expresses his personality perfectly through his driving.
Aggressive people make aggressive drivers. A Wall Streeter I once knew was a textbook narcissistic personality: extremely egocentric and entitled, and he reacted to criticism like Donald Trump. The one time I got a ride from him we were stuck in traffic and a car on a side street was trying to ease out onto our path. The narcissist said, "If that guy thinks he's going to pull in in front of me he's crazy," and moved his car as far forward as he could. He spoke with a tone of aggrievement, as if the other driver were personally insulting him.
I know a woman who only learned how to drive at age 35. When she drove, she would grasp the wheel in a sort of death grip and when on a highway would stay in the righthand lane and go 50 mph, even when all the other cars were going at least 60. While driving, she couldn't do anything else, like change a CD or even carry on a conversation. Not surprisingly, she had a tendency to find little things overwhelming in other areas of her life as well.
Is someone socially aware? They're more likely to be aware of what other cars in the vicinity are up to, too, and to drive defensively.
How do people react to frustration? If they do so poorly, you may get the full flavor of their personalities when they're stuck in traffic jams. They mutter and grouse and in general act as if the traffic jam was created just to frustrate them. (As in, "Why is this happening to me?") I knew one guy, who, when stuck in traffic, just blasted his horn to express his impatience. It served no purpose, as there was nowhere the people in front of him could have gone; it was just a reflection of his inability to handle frustration.
Likewise, road rage is never a separate, unrelated syndrome; it's just one facet of an overall anger management issue.
I've known two drivers who were probably organic sociopaths. (Meaning, neither was evil -- both were in fact generally good-natured. But both had a high threshold of excitement, i.e., it took more to get them excited about something.) Both, not coincidentally, drove too fast, partly because they enjoyed the sensation of speed, partly because they enjoyed the feeling that they were taking a risk.
One of them told me that once, while on a deserted stretch, he took his car up to 100 mph and then started to masturbate, as a sort of challenge to himself, just to see if he could get an erection while driving at that speed.
The other organic sociopath drove way too fast, too often. He once got something like eight speeding tickets in one year. On a few occasions he took his muscle car up to 140 mph on a straightaway where he knew no police cars could be hidden.
Once I was in a car with him on a winding two lane road where the cars were whizzing past each other at 50 mph with no center divider. When I expressed concern about a possible accident, he actually found my concern funny.
Both organic sociopaths scoffed if I played it safe at a stoplight. One would cup his genitals and say, "Nada." The other would make similar comments. One of these guys was a high stakes gambler, the other was attracted to physical danger.
(Strangely, I can also recall having been driven by two out and out sociopaths, and neither was a particularly bad driver in any way that I can remember.)
Is someone usually courteous? He probably lets other drivers cut in front of him as well.
Is someone able to take blame? The female Aspie I know once dented in the side of a car while rounding a cement-walled corner too soon. She described this as a "scratch." She also once rear ended an elderly driver when their light turned green. She explained this by saying, "He was too old to be driving! He shouldn't have been on the road! We had the green light! He took to long to react! The police officer said that there are a lot of accidents at that intersection!"
The other Aspie, if berated by another driver, would wag his finger at the driver, as if to say "Now now, you're the one who's at fault," even when he was clearly at fault.
I've never actually been driven by anyone who was a bad tailgater, though I seem to have met up with plenty of them on the highway. I would guess that they are pushy and aggressive all the time.
I've never known anyone who (wasn't handicapped who) parked in a handicap space. But I did know a woman who would regularly park in a 10 minute parking zone for an hour or so while she worked out. She was a slippery character in general. She hid money from her husband, and put spyware on his computer. She also had obvious implants, but denied that she had them.
If people are proud of their driving ability, they probably veer towards egotism in general.
Think of the people you know. Do any of them act out of character behind the wheel?