It is registered as a motorcycle in California. You do not need to wear a helmet or have a motorcycle endorsement because it is viewed to be in the "sidecar" class of motorcycle. Former Gov. Arnie famously talked his way out of a ticket at the Rock Store while riding his sidecar rig without a helmet or endorsement. I always wear a helmet, have an endorsement and avoid freeways whenever possible due to the large number of drivers trying to take your picture with their cell phones when they should be driving!
