This illusion of privacy is created by the engineering of cars themselves, but also by the speed. Once you start driving (or cycling) past 15 mph, you can no longer discern the faces of fellow road users. Thus, everything else out there is just another machine-bubble.
One of the reasons *some* drivers respond with rage to cyclists (purposefully trying to run them off the road, etc.) is that the cyclist reminds them that they are driving around 4000 lb machine that can kill them. Think about it: popular culture is replete with images of car crashes and their effects. Yet, we get in a car daily and drive them around and we have to forget how dangerous it can be to ourselves and to others.
In the US, the sight of a cyclist reminds the driver how vulnerable road users are. It's no longer about other machine-bubbles on the road, but ones with people in them and driving them. The people who react with aggression to cyclists - to the point of trying to harm them or driving aggressively around them -- are (to my mind, Vanderbilt doesn't say this exactly) people who are like abusers: when they see vulnerability in the person they are abusing, they want to hit them more.
The aggressive drivers will say it's because cyclists don't follow the rules. However, Vanderbilt points out that all car drivers break the rules every day. They drive over the speed limit, they drive unsafely around construction sites, they rarely come to a full stop at a stop sign, they speed up to go through yellow lights, the u-turn in the middle of streets, etc. I've forgotten the social-psychological term that he uses for this.
At any rate, Vanderbilt is fascinating on the psychology of driving and does a great job summarizing the research of that fella who wrote the tome on the high cost of parking lots. Forgotten his name.