I really do think this is the solution - if carpooling can be made as simple as checking a box, with time savings, and money savings, the only downside would be

I really do think this is the solution - if carpooling can be made as simple as checking a box, with time savings, and money savings, the only downside would be sharing a car, and a lot more people would do so. Demand and traffic would both be controlled by dynamically pricing 'private' vehicles. Your phone could also learn your departure time, and automatically determine when there are cars available / pricing is optimal to tell you to leave.