Personal vehicles have dominated the U.S. mobility system for nearly 100 years. But we are now in the formative stages of a powerful confluence of cultural, technological, and societal forces. It is possible that a new mobility system will emerge in the next few years that is superior to our existing system in almost every way. This report offers guidance on what to expect so that stakeholders can prepare today, and provides potential market sizes and plausible rates of mobility service proliferation that could occur under reasonable circumstances.