Why don't they go global? I'm guessing "money exchanged" is the problem, but I'd happily give away that[+]. Give me a reason to trust the "carpooler" and that's all I ask. Heck, allow me to easily coordinate with my colleagues, and that'd still be a gain.

[+] I don't care for the money, in the grand scheme of things you earn nothing from this, I'd rather have the gratitude of the rider; In fact, that's how I do it today when I pick a hitchhiker, I never take their money anyway.