The bill divides into two halves
Vehicle running costs split cleanly into those driven by distance and those driven by time. Fuel or electricity, tyre wear, brake wear and most servicing intervals belong to the first. Insurance, registration or road tax, depreciation, finance payments and periodic testing belong to the second, and they carry on whether the car moves or not.
The consequence is a poor economic position: a low-mileage second car often has a cost per kilometre several times higher than the main vehicle, because the same standing costs are spread across far fewer kilometres. Households frequently keep a car for occasional convenience without ever calculating what that convenience costs per use.
Depreciation does not pause
Value falls with age as well as with mileage, and for many models age is the stronger factor. A car kept for a year and driven very little is worth noticeably less at the end of it, and the low odometer reading recovers only part of the difference. Meanwhile a second car in a market moving away from its type can lose value faster while stationary than a well-chosen car loses while working.
This is the invisible part, since nobody sends an invoice for depreciation, a point developed elsewhere on this site. What matters here is only that the invisible cost is not suspended by disuse. It is arguably the largest single item on a standing-cost list.
Standing still causes its own damage
Mechanical sympathy for an unused car is misplaced. Batteries discharge and sulphate. Tyres develop flat spots and lose pressure, and their rubber ages on a clock unrelated to tread depth. Brake discs corrode where pads rest against them, and the first drive after months of standing can leave a permanent scoring. Seals and hoses dry out. Fuel degrades. Rodents find engine bays attractive and wiring edible.
Modern vehicles add electronic problems to the mechanical ones, since numerous systems draw a small current continuously and a flat battery in a car full of control modules is a more expensive event than it used to be. Regular short use, ideally long enough for everything to reach operating temperature, prevents most of this. A car used once a month for ten minutes gets close to the worst of both worlds.
Cover while off the road
Cancelling insurance on a car that is not being used is an obvious saving and it is not always available or wise. Where a vehicle is kept on a public road, most jurisdictions require it to remain insured regardless of whether it moves, and enforcement is often automated against a central database. Many markets provide a formal declaration that a vehicle is off the road, which suspends certain obligations, and the rules for it differ everywhere.
There is also the question of what the car is exposed to while parked. Fire, theft, vandalism, flood and a falling tree are perils that do not require the vehicle to be moving. Laid-up cover, which insures a stationary vehicle against those events without providing road cover, exists precisely for this situation. And a gap in cover has a further effect: continuous insurance history is itself a rating factor, and a break can cost more later than it saved at the time.
The second-car question, asked properly
The honest way to evaluate an occasionally used vehicle is to add the standing costs for a year — insurance, tax, testing, finance if any, and a realistic figure for the value lost — and divide by the number of journeys it genuinely enables that could not have been made otherwise. The result is frequently uncomfortable.
That does not make it the wrong decision. Availability has real value, particularly where public transport is poor, where work is irregular, or where a household depends on being able to move two people in different directions at once. The point is only that the value should be weighed against a number rather than assumed to be worth whatever it costs.
Bringing one back
A vehicle returning to use after a long period deserves a check before it carries anyone at speed. Tyre pressures and condition including the sidewalls, brake operation on a slow first drive, fluid levels, the state of the battery, and whether the periodic roadworthiness test is still valid. Rules on testing vary by jurisdiction and must be checked locally, as does whatever registration formality applies.
An unroadworthy vehicle is also an insurance problem, because most policies contain a condition requiring the car to be maintained in a roadworthy state. That is a genuine route to a reduced or refused claim, and it is one of the more avoidable ones. An afternoon of checks is a small price for removing it.
