Assuming that it is even necessary to use ethereum for a distributed uber -- I see no need for the driver to maintain a copy of the blockchain, and certainly not in the vehicle. Groups of drivers who trust each other IRL could, for example, cooperate to finance a single full node and then make calls to that service to verify payment.

Presumably, drivers could also use third-party mapping software / services, dispatchers, whatever aspects of the biz are not handled by the decentralized protocol.