Back in 2012, California adopted legislation, rules of the road so to speak, for the operation of autonomous vehicles on Golden State roadways. It took three more years, until 2015, for implementing regulations to follow.
No rules covered the hauling of autonomous freight — specifically trucks exceeding 10,001 pounds because they didn't exist. The inspection regime for trucks was another reason. The California Highway Patrol needed to be consulted, so the issue was put off.
