Google plans to roll out 100 prototype self-driving vehicles later this year, but some states are finding it hard to write rules of the road for vehicles that lack a steering wheel or pedals, NBC News reported. Advocates of the vehicles say the cars will save lives, reduce congestion and make it easier for those who can't drive to get around, but state regulators have raised concerns about having a fleet of computer-directed vehicles roaming the streets without any controls for a human driver. Nevada, Florida and Michigan have approved driver-less cars, as has California, where Google is based. But California law requires that a test driver be in the vehicle in case something goes wrong, a regulatory challenge that Google will likely face into the future as it looks to market the cars to consumers across the country.