Earlier quoted context omitted.
That's 500k vehicles not 500k people. While the plurality of vehicles could be single-occupant passenger vehicles, a good chunk of those vehicles are freight, multiple-occupant passenger vehicles, and some are even busses.
Being someone that has sat in a lot of traffic in Texas on these interchanges, the number of vehicles with more than one person is a rounding error. There's a few trucks hauling freight, but they try to miss the cities during rush hour.
In fact there are so few people in the HOV lane that I always feel like I'm doing something wrong when I take it, like I misunderstood the rules. It can't be this easy.
Nah, I really am the only person on the highway with more than one person in the car.