I don’t think it’s the number of people transported that is hard to get one’s head around—it’s imagining using a subway to get to all of their destinations which are spread all over and separated by at least a quarter mile of parking lots and 8 lane highways. In their mind, this would require an absurd amount of subway or bus lines and tons of transitions and it would take an eternity to get to their destination and they might interact with lower class people and so on. The thing they don’t understand is that without cars you can build all of those destinations much closer together in a single walkable place that you just need transit to get to/from. When you take away the cars, you don’t need gargantuan parking lots or 8 lane highways.