Bobtail protection is analogous - it insures the truck although "bobtailing", meaning working without having a trailer attached. So for those who crash the tractor although bobtailing to have repairs, Bobtail insurance pays for damage and injuries. However not required, NTL and Bobtail policies give affordable liability safety for California https://www.amazon.co.uk/gp/product/B0D4MRHZL9