So are you going to get up and drive into work with me at 0630 and then leave work at 1630, well unless it is 1730 due to a deadline or schedule shift, and then go with me to do some shopping after work, run to a buddy's house to pick up that jacket I left last weekend, then get home at a reasonable time to have dinner with the kids?
Carpooling sounds so....so "progressive" until one actually has to practice it. For the majority of the people I know it is extremely impractical.
That's why a bus or train makes more sense. They have multiple vehicles with set schedules and heck, you can meet your friend for lunch

And really, how often do you leave your jacket at a friends house?
One of the cooler things about DC riding were the slug lines. You just wait for someone who wants to use HOV to pull up who's going in your general direction and hitch a ride to work. Same on the way home. Then you can have your alternate schedule without having to have a regular car pool to deal with. When you have to drive (to get a jacket from your friend's house or work late), you pick up a slug or three. When you don't have to drive, you hit the slug line and ride to work for free.
Carl