You're absolutely right, and this is the problem. In aggregate, they are horribly inefficient. At the level of the individual, they're generally much much faste

You're absolutely right, and this is the problem. In aggregate, they are horribly inefficient. At the level of the individual, they're generally much much faster and convenient than other options (i.e., public transit), even accounting for traffic. So -- in game theory terms -- many people defect. One of the reasons is frequency. Depending on time of day, a subway or bus may not come for 10 minutes. A car is basically infinite frequency: when you want to go, you go right away. The other is more direct routing. To get to my favorite bookstore, about 5 miles due north, on transit takes an hour because I either have to take the rail into the city center first and transfer (or take one of the most infrequent and slow bus routes in the system). It's maybe 35 minutes by bike or car, as long as it's not rush hour. I don't own a car, but I can't say I wouldn't be tempted some days, if I did.