Woodland Hills-based 21st Century Insurance Co. is the latest company to start basing its auto insurance premiums off a motorist’s driving record instead of where he or she lives. The change will result in a 12 percent reduction in premiums for drivers in Los Angeles, a saving of $218.72 annually. The overall statewide savings amounts to $60.5 million. Insurance companies in California and elsewhere have long used a motorist’s ZIP code in determining how much he or she will pay for car insurance. The rates will now be determined by driving record, driving experience and the amount a motorist drives.