6.4 Part C Uninsured/Underinsured Motorists

Why Part C Exists

Part A pays the other party when the insured is at fault. But what happens when someone else causes the crash and that driver is uninsured or underinsured? Part C — Uninsured/Underinsured Motorists fills that gap. It is first-party coverage (it pays the insured), yet it is fault-based: the insured collects only by establishing that the other driver was legally liable.

UM/PD (uninsured motorist property damage) is available in some states to cover the insured's vehicle damage from an uninsured driver, often with a deductible; in many states only UM bodily injury is offered.

Hit-and-Run and Phantom Vehicles

A hit-and-run driver who flees and cannot be identified is treated as an uninsured motorist under UM. The classic tested rule: most states and the ISO form require actual physical contact between the hit-and-run vehicle and the insured (or the insured's vehicle) for UM bodily injury to apply.

A phantom vehicle — one that causes an accident (e.g., runs you off the road) without ever touching you — is frequently excluded unless the state has adopted broader rules or corroborating evidence requirements. Examiners use the 'no-contact' miss-and-run scenario to test this limitation.

UM/UIM is first-party, so the insured does not sue their own insurer for negligence — they pursue the contractual UM benefit, often through arbitration when the insurer and insured disagree on fault or the amount owed.

The Underinsured (UIM) Gap Calculation

UIM is the trickier computation. The dominant approach is the difference (gap) method: UIM pays the shortfall between the insured's UIM limit and the amount the at-fault driver's liability insurer paid.

Worked example — gap/difference state. The insured suffers $120,000 in proven BI damages. The at-fault driver carries $50,000 liability and pays it in full. The insured's UIM limit is $100,000.

UIM brings the insured up to their own $100,000 UIM limit, not to the full $120,000 loss. A minority of states use an excess (add-on) approach where UIM stacks on top of the other driver's limit. Always note: UIM requires the at-fault driver's limit to be lower than the insured's UIM limit to trigger at all.

Mandatory Offer, Stacking, and Exclusions

Mandatory offer

Most states require insurers to offer UM/UIM with every auto policy. The insured may reject it, but typically only in writing; absent a valid written rejection, UM/UIM is read into the policy at limits often equal to the liability limits.

Stacking

Where permitted, stacking lets an insured combine UM/UIM limits across multiple vehicles on one policy or across multiple policies, multiplying available coverage. Many policies and states contain anti-stacking language; whether stacking is allowed is state-specific.

Key Part C exclusions

• Bodily injury to an insured occupying or struck by a vehicle owned by the insured but not insured for UM/UIM under the policy (the owned-vehicle exclusion).
• Claims settled without the insurer's consent that prejudice its subrogation rights against the at-fault party.
• Use of a vehicle as a public livery conveyance.
• Punitive or exemplary damages, where state law allows their exclusion.

UM vs. UIM, Bodily Injury Only, and Reduction Clauses

Part C splits into uninsured motorist (UM) and underinsured motorist (UIM) coverage, and the exam tests the trigger for each. UM responds when the at-fault driver has no liability insurance, is a hit-and-run/phantom vehicle, or whose insurer is insolvent. UIM responds when the at-fault driver has insurance but with limits lower than the insured's damages — it fills the gap between the other driver's limit and the insured's UIM limit.

Most states' UM/UIM covers bodily injury only; property damage to the insured's auto is handled under collision (some states offer optional UMPD). A heavily tested mechanic is the UIM gap calculation: if the insured carries $100,000 UIM and the at-fault driver carries $25,000, the insured recovers the $25,000 from the other carrier plus up to $75,000 from UIM, depending on whether the state uses a difference-in-limits or excess approach. Because UM/UIM must be offered with every auto policy and can be rejected only in writing, the mandatory-offer rule is itself an exam point.

Why the State Mandates an Offer

The exam frames UM/UIM as consumer-protection coverage the legislature insisted on because compulsory liability laws never reach every driver — uninsured rates run high in many states, and minimum limits are often too low to cover a serious injury. That is why insurers must offer UM/UIM with limits at least equal to the policy's liability limits, and an insured can decline or reduce it only by a written rejection that the insurer must retain.

Absent a valid written rejection, courts frequently reform the policy to provide UM/UIM at the full liability limit, a fact pattern that appears in scenario questions about a driver who never signed a waiver.