In most cases, drivers and vehicle occupants involved in a crash can rest assured that help will soon be on the way. Even if they aren't able to call 911 on their own, the crash or its aftermath is typically witnessed by other motorists, who can then report it.

Sometimes, however, others may not be aware that a crash has occurred. There are plenty of examples of drivers who endured several days trapped in a wrecked vehicle before they were discovered.

In the summer of 2017, a 70-year-old woman in Washington State subsisted on two bananas and a small amount of water for five days after her vehicle crashed over an embankment. Earlier this year, a woman survived seven days on her own after driving off a seaside cliff in Big Sur, Calif.

Vehicles can easily be camouflaged by underbrush and other obstacles after a crash, even if the wreck occurs in a well-traveled area. In April, a man who crashed near a highway exit ramp in Maryland said he called for help, but that no one could hear him due to the noise of the road. His vehicle, which crashed into a ravine, wasn't visible from the road and he wasn't found until two days later by a highway crew.

Automatic crash notification systems in vehicles are meant to prevent such nightmarish situations from occurring. They can also be essential for quickly dispatching emergency crews to the scene of a crash, increasing the chance that any seriously injured occupants will get the medical attention they need.

As the name suggests, an automatic crash notification system will send out an alert if it senses that a vehicle has been involved in a serious crash. The National Highway Transportation Safety Administration says the system's sensors will detect when the vehicle's airbags have deployed or when its speed has suddenly dropped to zero due to a crash.

When the system determines that a crash has occurred, it will alert an operator to the situation. This operator can directly communicate with the vehicle's occupants through the system, and can also direct emergency responders to the scene.

Some vehicles have advanced automatic crash notification systems, which collect a larger set of data to determine how severe the crash is. APCO International, a public safety communications company, says these sensors can determine if the vehicle rolled over and help assess how severe the occupants' injuries are likely to be. This information, in turn, can help direct emergency responders in deciding what resources need to be deployed and where injured occupants should be transported for treatment.

Improving emergency response is a key benefit of automatic crash notification systems. Sanjay Salomon, writing for the Boston Globe, says a 2013 study by the NHTSA determined that crashes were reported within two minutes for all vehicles equipped with the system, while 20 percent of vehicles without the system did not have a crash reported for five minutes or longer.

This faster response is particularly important in rural and less traveled areas, where it may take several minutes for another driver to come upon the crash scene. The NHTSA says the systems can also help pinpoint the exact location of a wreck if the vehicle leaves the road in a remote area.

The Insurance Institute for Highway Safety says that while automatic crash notification systems have the potential to prevent fatalities on the road, they also have certain disadvantages. The institute says the system will only be relevant in a small number of crashes, since most incidents will be witnessed by other drivers or reported by a driver involved in the crash.

The system also tends to come at a price. It may only be included as part of a larger package, such as navigation and infotainment features, and a subscription fee may be required. For example, the OnStar system which first debuted in General Motors vehicles in 1996 has a monthly cost of about $25.

Automatic crash notification systems are often available as an option on newer vehicles. Drivers should consider whether the added security of the system is worth the price.