A highway lane of car traffic transports far more people than a single rail line.
I don't think this is in any meaningful way true. Typical theoretical rail capacity per unit land area is 5-10 times that of human piloted highway systems.
I thought I read something about this somewhere... but now that I think about it, it doesn't make sense to me. I'll correct that. This report seems to cover the issue of rail capacity (looks interesting; I should probably read it more closely). It seems to say 15k-50k passengers/hr of capacity, depending on vehicle type and train length. Reversing the numbers on this page imply that a highway lane has a capacity of 1.5-1.7k. So yeah, I'm just totally wrong.