Addiction to speed is a part of it. I think being trapped in a car actually creates a lot of psychological issues. Another one that doesn't get mentioned enough IMO is claustrophobia. All these psychological issues are probably big contributors to road rage.

I have a more metaphysical take on it: One's level of suffering is proportional to the distance between where one's body is located, and where one's mind is. It applies in a lot of different scenarios, and I think is kind of the secret behind the mindfulness movement. (If your mind and body are in the same place, you are much happier.)

The way that this applies to cars is in two ways: 1) The driver's body is physically located in a torture chamber, essentially. Sure, they put in a cushy recliner, and an entertainment system, but those can only do so much to mitigate how awful it is to drive. 2) The speed of the car promises a quick trip, so the driver's mind is already at their destination, and the separation makes them miserable and furious.

Yeah, yeah, that's pretty woo-woo. It's just a metaphor for the impatience drivers feel because, in their minds, they're already walking in the door, they're already ordering food at the restaurant, they're already kissing their spouse, they're already answering work emails, or whatever it is they have at the destination. And you, pedestrian, you are directly responsible for keeping them from it.

But I notice the real effects myself. Last weekend, I went up north to my vacation spot, where I've found that riding my bicycle to the beach is subjectively much faster than driving. It's almost like teleporting! Objectively, it takes longer, but when I'm riding my bicycle, I'm mentally on the road riding my bicycle, so the trip doesn't even register as part of the beach experience the way driving does.

I don't think speed is the main factor, I think it's entitlement. With public transportation, you might have to go somewhere specific to get your ride, rather than it being just outside. Then you wait til a certain time, share the ride with others, the path and speed arent in your control so it may not be the most efficient route. With a car, you can go when you want, where you want and how you want. Until you know, others get in the way. If something is making you drive slightly slower, you now have less control.

I also think driving in general is an unpleasant experience. For most of the time driving, you are staring at asphalt, concrete and other cars, nothing is fun to look at. You have to focus constantly and any distractions become annoyances. Because of cars everything is so far away it always requires the car to do ANYTHING. For all the supposed freedom, you are constantly being told what to do. This is the speed limit, this is a stop sign, this is your designated lane, you have to yield. At every point you run into people and the more you run into the less you can do what you want. And those people can act like don't understand rules, aren't paying attention, interpret the rules differently, think they don't apply to them, know they can get away with it because the rules aren't heavily enforced or they are selectively enforced. Sometimes the rules don't always make the most sense, they are the way they are so it's easier to assign blame to someone in a insurance claim or court case. Or sometimes the rules make sense for someone else, but not your entitlement machine.

I have become convinced that people get addicted to speed.

While that part is certainly true, the modern homo sapiens automobilis seems more addicted to crawling along in slow moving traffic while hating everyone moving faster or able to escape in any way.