In general, Supplementary Uninsured/Underinsured Motorist (SUM/UM) coverage applies if another driver who causes an accident has little or no automobile insurance coverage. For example, if you have been injured by another driver who has a $25,000 liability insurance policy but you carry $100,000 of SUM coverage, you can pursue a claim against your own policy (or the policy of a family member who lives with you) for the difference, in this example $75,000, to help compensate you for the injuries you’ve suffered.