In some cases if you add a second driver it can cost you more, especially if that driver is young or has a bad driving record. There are many policies, where if the driver you are adding has as good of record as you, may not cost you anymore.
If you own a "classic car" you may be able to get cheap insurance if you only do limited mileage each year. Often many companies have special rates for thsi type of vehicle especially if it is not your main car.
A lot of car insurance companies are now looking at customer's credit ratings, so if you have a good credit score you may benefit from lower premiums.
