It's an unpleasant experience many drivers have encountered. You pull into a parking lot, leave your vehicle, and notice a hissing sound. You've had the misfortune to run over a nail on the road, and one of your tires is going to be flat by the time you're doing shopping.

Fixing a flat tire is something many drivers know how to do. You simply put on the spare tire and make a note to visit a mechanic who can patch the damaged tire.

So it can be another unpleasant surprise if you look through your vehicle and discover that no spare tire is available. This is the situation on more than one in four new vehicles, according to AAA.

The organization recently determined that 28 percent of 2017 model year vehicles don't have a spare tire as standard equipment. Automakers that leave out the spare tire typically do so in an effort to reduce the vehicle's weight and improve its fuel economy. AAA said it responded to more than 450,000 flat tire calls in the United States last year where a spare tire was unavailable.

AAA's analysis of 2017 model year vehicles determined that spare tires were offered only as optional equipment on 44 models. Another 52 models did not have a spare tire available at all.

AAA conducted similar research in 2015. In that study, the organization determined that the share of vehicles without a spare tire as standard equipment had increased from 5 percent of 2006 model year vehicles to 36 percent of 2015 model year vehicles.

"Having a flat tire can be a nuisance for drivers, but not having a spare could put them in an even more aggravating situation," said John Nielsen, AAA's managing director of automotive engineering and repair. "This can turn the relatively routine process of changing a tire at the roadside into an inconvenient and costly situation that requires a tow to a repair facility."

Vehicles that have eliminated the spare tire will include a tire inflator kit as a substitute. This device is designed to temporarily seal a puncture and restore air pressure, allowing a driver to bring the vehicle to a mechanic for a more permanent repair.

However, AAA tests found that tire inflators are only effective if the puncture occurs in the central tread and the object remains embedded in the tire. Researchers determined that the kits could not be used to repair tires with punctures in the sidewall or damage caused by potholes or curbs. They also could not be used to fix a tire after a blowout.

AAA found that tire inflator kits can be up to 10 times more expensive than a spare tire, since they require the replacement of the kit and tire pressure monitoring sensor after use. The kits also have an expiration date and typically need to be replaced after four to eight years. Spare tires will also expire, but it typically do not need to be replaced until they are 10 years old.

Flats are more likely to occur if a tire is underinflated, so it is important to check the pressure of each tire regularly. Many vehicles have tire pressure monitoring equipment to let you know when a tire needs to be inflated. If your vehicle has a spare tire, make sure to keep that inflated as well.

Don't assume the vehicle has a spare tire, and make sure to ask if a spare is available when purchasing a vehicle. If your vehicle has a tire inflator kit, read the owner's manual to understand how it works. You'll also want to check the expiration date to see when it needs to be replaced.

"With low-profile tires and the elimination of a spare tire, many newer vehicles are especially vulnerable to roadside tire trouble," said Nielsen. "AAA urges drivers to make it a priority to check their vehicle's equipment and know what to do if faced with a flat tire."