To the list of items you should no longer expect to see in a new car — those once-common features like a metal ignition key, an ashtray or a vent window that swings open — you may soon be adding the spare tire.

Already, nearly a third of the 2017 models offered in the United States do not come outfitted with a save-the-day spare as standard equipment, according to a recent study by AAA.

In truth, the extinction of the spare tire has been happening, if gradually, for years. Full-size spares gave way to the space-saving “doughnut” versions you sometimes spot on vehicles traveling at worrying speeds. They, in turn, are yielding their under-floor real estate to no tire at all.

The elimination of the spare by automakers is not entirely an abandonment of good sense or a severe example of cost-cutting; in fact, it can benefit drivers. The primary goal is weight reduction, a crucial factor in meeting fuel economy standards.