Uninsured vs. underinsured: a vehicle with no liability insurance is uninsured. An underinsured motor vehicle is insured, but for less than the uninsured motorist limits carried by the injured person (§11580.2(p)(2)). California compares limits to limits, not limits to damages, so a vehicle with limits equal to the insured's UM limits is not underinsured even if the damages are larger.

How much underinsured coverage pays: under §11580.2(p)(4), the most the insurer owes is the insured's underinsured motorist limit less the amount paid by or for the person legally liable. It is not added on top. Example: a $100,000 limit and a $50,000 payment from the at-fault driver's insurer mean at most $50,000 more. Under (p)(3), the coverage applies only after the at-fault limits are exhausted by payment.

Hit-and-run and stacking: a vehicle whose owner or operator is unknown counts as uninsured only if (§11580.2(b)): - the injury arose out of physical contact with the insured or the insured's vehicle, - the accident was reported to police within 24 hours, and - a sworn statement was filed with the insurer within 30 days. A car that forces the insured off the road without touching does not qualify. Under §11580.2(q), limits for two or more vehicles or policies may not be added together (no stacking), whatever premiums were paid.

Property damage (§11580.26): - Uninsured motorist property damage (UMPD), for a policy without collision coverage, pays for damage to the insured vehicle up to its actual cash value or $3,500, whichever is less. It does not include personal property in the vehicle or loss of use. - The collision deductible waiver, for a policy with collision coverage, pays the collision deductible in a collision with an uninsured motor vehicle. Both require actual, direct physical contact, an identified owner or operator or a license number, and a report to the insurer or its agent within 10 business days. Neither applies to an unidentified vehicle.