In Pennsylvania automobile insurance law, purchasers of insurance have the option to "stack" uninsured and underinsured motorist coverage. If you choose "stacking," this means that you can add the coverage together for each vehicle you have insured, at least under the policy. (An issue presently exists as to whether you can "stack" coverages under separate policies of insurance.) For example, if you have two vehicles, with $100,000/$300,000 (meaning $100,000 available per person, and $300,000 available per accident) in uninsured or underinsured motorist coverage, you can "stack" the coverages and have available $200,000/$600,000 in coverage.
Practice that increases the money available to pay auto liability claims. In states where this practice is permitted by law, courts may allow policyholders who have several cars insured under a single policy, or multiple vehicles insured under different policies, to add up the limit of liability available for each vehicle.