The California Air Resources Board Off-Road Heavy-Duty Diesel Equipment (In-Use) Regulation mandates that any person or entity that owns, leases, rents or sells any diesel-fueled off-road vehicle/equipment operating in California must reduce fleet wide emissions by retrofitting, repowering, or replacing equipment with cleaner technology and/or engines. Off-road vehicles are those vehicles that were intended to be used off-road and cannot be registered for on-road use.