Google's patented this idea; see, e.g., http://arstechnica.com/gadgets/2014/01/google-patents-ad-powered-taxi-service-that-would-offer-free-rides-to-shoppers/ h

Google's patented this idea; see, e.g., http://arstechnica.com/gadgets/2014/01/google-patents-ad-powered-taxi-service-that-would-offer-free-rides-to-shoppers/ http://arstechnica.com/gadgets/2014/01/google-patents-ad-pow...