The cost of ambulance rides adds up. In 2011, the United States spent about $14 billion on ambulance services, $5.3 billion of which Medicare paid for. Many of those trips might not have required an ambulance. Estimates of inappropriate use vary, but most are around 30 percent.

Although it’s not always clear when an ambulance is warranted, there is evidence of waste and fraud in the industry. Last year, ambulance companies collectively billed Medicare improperly for at least $700 million.

In 2014, employees of a Philadelphia-area ambulance company received prison sentences for fraudulent bills. That same year, the owners of a Tennessee company were convicted of fraudulent ambulance billing. A 2015 O.I.G. report found that half of questionable billing of Medicare by ambulance companies is from four metropolitan areas: Philadelphia, Los Angeles, Houston and New York.

Other recent evidence from New York suggests a substantial number of ambulance rides are taken for non-emergencies. Scholars from Georgia State University and the University of Colorado Denver studied ambulance rides in New York before and after the Affordable Care Act’s coverage expansion. After the expansion, dispatches for minor injuries rose considerably while those for more severe ones did not.

By 18 months after the expansion, ambulance dispatches for minor injuries were up 150 percent.

An explanation for the results is that a person’s insurance coverage tends not to affect a decision about calling an ambulance in a real emergency. But for minor injuries, people are more likely to call an ambulance if they have coverage than if they do not, even if they don’t really require that level of care.

Using an ambulance also diverts attention and resources from true emergencies. Response times are longer than they could otherwise be if ambulances were used only when needed. One study found that the Affordable Care Act, by expanding coverage and financial access to ambulance rides, slowed ambulance response times by 19 percent. Uber and Lyft can’t disobey traffic laws the way ambulances can to speed people to a hospital in urgent situations. But they can broaden transportation options for patients and could disrupt the ambulance market. Both have announced new services to provide rides to medical appointments. This kind of non-emergency medical transportation is something many health plans already provide, but Uber and Lyft may be able to do it more cheaply, with better customer service and less waste. Uber Health would allow health care providers to order rides for their patients. As of March, over 100 health care organizations were using the service. Lyft Concierge is similar and already being used by a number of organizations that arrange rides for people in need of care. Of course, patients can request Uber or Lyft rides on their own, instead of an ambulance. And these services could help patients avoid missing appointments because of lack of affordable transportation. They may also help patients receive care in more appropriate and lower-cost settings, like a doctor’s office instead of an emergency department. One study found that Uber’s entry into a city reduced ambulance use by 7 percent. An advantage of arranging your own ride is that you can direct it to a hospital or doctor’s office of your choosing. In contrast, ambulances take patients only to hospitals — and typically to the nearest one, whether the patient would prefer that or not. This can actually degrade care. Evidence suggests that patients who return to the hospital where they received major surgery have a lower risk of mortality than if they go to another hospital. With an ambulance, there is no guarantee you’ll return to the same hospital. Although lack of affordable transportation is one barrier to care, it isn’t the only one. A randomized study of Medicaid patients at two Philadelphia-area clinics found that offering Lyft rides did not change missed appointment rates. Patients may miss appointments for other reasons, such as being unable to get off work or to obtain child care.