Comprehensive vs collision coverage

Liability coverage pays for what you do to other people. Comprehensive and collision pay for damage to your own vehicle, and together they are what people mean when they say full coverage. They are sold as two separate lines on the declarations page, each with its own deductible, and a car can carry one without the other. That is unusual in practice, because lenders require both, but it becomes a real choice once a car is paid off and has aged.

The two are distinguished by cause. Collision is damage from your car striking something or being struck: another vehicle, a pole, a guardrail, a pothole hard enough to bend a wheel, or a rollover. Comprehensive is nearly everything else that can happen to a parked or moving car that is not a collision: theft, vandalism, fire, hail, flood, a falling tree, a cracked windscreen, and a collision with an animal. Understanding which line responds to a given event is what lets you set the two deductibles sensibly and decide whether to keep each.

Collision: the impact line

Collision coverage pays to repair your vehicle after it hits or is hit by another object, regardless of fault, less the collision deductible. If the other driver was at fault, your carrier will typically pay your claim first, then pursue the other driver's carrier through subrogation and refund your deductible when it recovers. That is the practical reason to carry collision even when you are a careful driver: it lets you fix your car on your own carrier's timetable rather than waiting for a liability dispute to settle.

It also responds when there is no one else to pursue. A single-car accident on an icy pass, a scrape against a parking garage pillar, a hit-and-run where the other driver is never identified, and a rollover on a dirt road are all collision claims. In some carriers' forms a collision with an animal is moved to comprehensive, which matters on the deer and elk corridors of northern Arizona, Utah and Idaho; ask which line your form uses.

Collision is the more expensive of the two lines because the events it covers are the ones drivers cause, and the premium tracks the driving record, the annual mileage, the vehicle's repair cost and the deductible chosen.

Comprehensive: the everything-else line

Comprehensive, called other-than-collision in some forms, pays for loss to your vehicle from causes that are not an impact while driving. It is largely priced on where the car lives and what it is, rather than on how it is driven: theft rates in the area, hail frequency, wildfire and flood exposure, and how attractive the model is to thieves. A car garaged in central Phoenix or Las Vegas carries a different comprehensive premium from the same car in Boise for those reasons, while the collision premium moves less.

In the four states we work in, comprehensive is the line that responds to the region's particular hazards: monsoon hail and flash flooding in Arizona, dust-storm sandblasting and windscreen damage across the Southwest, wildfire and smoke damage on the urban edge, snow load and falling branches in Utah and Idaho winters, and catalytic converter theft everywhere. Glass is often given its own treatment, either a separate lower deductible or full glass coverage with no deductible, and in a region where windscreen chips are routine that endorsement is worth pricing.

The mechanism that differs: cause, deductible and price

Both lines settle the same way. The carrier pays the cost to repair, or if repair would cost more than the vehicle is worth, pays the actual cash value of the car immediately before the loss, less the deductible and less any salvage you keep. The differences are upstream of that: which event triggers which line, which deductible is subtracted, and which premium you paid for the privilege.

Because comprehensive claims are less often the driver's doing, many carriers do not surcharge the premium after a comprehensive claim the way they do after an at-fault collision claim, though a run of them can still affect renewal. That asymmetry is a reason people set the comprehensive deductible lower than the collision deductible: a hail claim is not going to raise the rate much, so a low deductible is cheap to use, while a collision claim is expensive twice over.

A worked claim

Suppose a driver in Tucson carries a $500 comprehensive deductible and a $1,000 collision deductible on a car worth $18,000. In August a monsoon storm drops hail that dents every panel and the repair estimate is $6,500. That is a comprehensive claim: the carrier pays $6,000 and the driver pays $500. Two months later the same driver rear-ends someone at a light and the estimate is $4,200; that is collision, the carrier pays $3,200, the driver pays $1,000, and because the driver was at fault the renewal premium is likely to rise.

Now suppose instead that a flash flood on a low crossing pushes the car into a concrete barrier and fills the cabin with water. Most forms treat the flood as the proximate cause and the whole loss as comprehensive, so the lower deductible applies even though the car also struck something. Say the total repair estimate is $16,000 against an $18,000 value; the carrier will usually declare the car a total loss, since repair plus salvage value approaches the car's worth, and pay $17,500. The numbers are for illustration; the point is that which deductible applies is decided by the cause the adjuster records, and that a borderline event is worth describing carefully and completely.

Who needs which

Lenders and lessors require both, so the decision only arises on a car you own outright. Then:

• Keep both on any car you could not replace from savings without hardship. The premium for the pair is the price of not having to.
• Keep comprehensive and consider dropping collision on an older car in a hail-, theft- or wildfire-exposed area; comprehensive is usually the cheaper of the two and the events it covers do not care how old the car is.
• Consider dropping both on a car whose value is low enough that a year of premium for the pair is a large share of what a total loss would pay. The rule of thumb is to compare the annual premium for the two lines plus the deductible against the car's actual cash value; when the first figure approaches the second, the coverage is buying very little.
• Do not drop collision because you rarely drive; the hit-and-run and the uninsured driver who hits your parked car are collision claims, and a low-mileage discount already prices your driving.
• Do not drop comprehensive on a car parked outdoors in a high-theft area or under trees, whatever its age.

Setting the two deductibles

There is no requirement that the deductibles match. Set the comprehensive deductible at a figure you would be willing to pay for a windscreen or a hail claim without hesitation, and set the collision deductible higher, at a figure you can pay from savings on a bad day, since raising it moves the premium more and the events it covers are rarer for a careful driver. Then price the glass endorsement separately; in the desert it often costs less than one windscreen. Vanishing-deductible features, where the deductible falls each claim-free year, are worth having if offered but are not worth switching carriers for.

When the answer is to keep what you have

If the car is financed, leased, less than a decade old, or the only vehicle in the household, the answer is almost always to keep both lines and adjust the deductibles rather than the coverage. Dropping either to save premium is a decision that looks fine until the year it does not, and the annual saving on an older car is often smaller than people expect once the premium is broken down by line. Ask for that breakdown. We do it for drivers in Arizona, Nevada, Utah and Idaho from the declarations page, show the cost of each line against the car's current value and the household's savings, and if the existing structure is right, we say so and change nothing.