You're ignoring space between cars, even with full automation you can't have a highway full of cars with no space between them, else there'd be no room for cars

You're ignoring space between cars, even with full automation you can't have a highway full of cars with no space between them, else there'd be no room for cars to merge on/off the freeway, and any traffic disruption would cause an immediate traffic back-up. Add one car length of distance and that puts the train in the same ballpark as the freeway lane. (I'll ignore the challenge of filling the Corolla with 5 people - I don't want to be the guy stuck in the middle seat) Though the problem isn't just throughput of the freeway, but also a question of where all of those cars are going to go when they get to the destination -- generally the commute traffic is going the same place at the same time. Self driving cars may not need a parking space, but if they are going to drop off passengers and then drive away to park somewhere outside of the city center, that causes even more city traffic. because they need to stop to let passengers off and on. At rush hour, the rate of the subway system is basically limited by how quickly people can flow from the platform into the train. That's why large train stations have multiple tracks.