A visit to an emergency room can mean a lot of different things: fear, anxiety, pain, maybe even annoyance. But almost everyone can count on one consistent feature: waiting.

In a 2014 study, the Centers for Disease Control and Prevention reported that ER wait times average about 30 minutes, and overall treatment times average about 90 minutes.

Beyond that, ProPublica compiled treatment times for ERs in all 50 states, and found some patients aren't sent home for closer to three hours. Even patients with broken bones can wait an hour to get pain medication.

While this might be anywhere from agonizing to irritating, there are a number of actual reasons why ER wait times are so long. 

In a video uploaded to YouTube in February, Toronto ER doctor Mike Evans explained that the reason why you can sit around for hours in an ER, despite obviously being sick or injured, stems from how emergency medicine works in the first place.

Describing the ER as a place with "an incredible mix of injuries and illnesses," Evans lays out how an ER is connected to every other part of the hospital, involving a mix of doctors, nurses, experts, and laboratories. Coordinating all of these elements is a difficult job that requires scheduling precision, and any one of them can have a delay, from a long line to use a piece of equipment to a staffing issue. 

ER needs are always changing, often minute by minute, and a patient coming in during a heart attack or with a critical injury will always take priority over someone with moderate pain or a less severe injury. 

The nature of how ER's handle patients developed because of the nature of emergency medicine itself, Evans explains. The sorting of patients by the severity of their problem began in the 1790's, after Baron Dominique Jean Larrey, Napoleon's Surgeon in Chief, needed a way to prioritize the massive numbers of casualties coming back to his clinics, as his hospitals were overwhelmed. 

In his memoirs, Larrey wrote that young army surgeons must carry everything needed "to afford the wounded speedy assistance." The process he pioneered to do that became known as triage, after the French word "trier," meaning "to sort." It involved a system of ambulance corps, field hospitals, and specialized drivers and stretcher bearers, all designed to offer assistance to the most wounded first, no matter their rank or location.

The modern ER's specialization and prioritization has its roots there. But while Larrey's triage system was designed to handle mass casualty waves, modern ER overcrowding has only increased, contributing to ever-lengthening wait times.

A 2012 study published in "Transactions of the American Clinical and Climatological Association" found myriad reasons for the problem of long waits at overcrowded ER's. Some of these include the federal mandate that any patient who goes to an ER must be treated, patients being "boarded" in the ER while waiting for regular rooms to open up, and staffing shortages. Another factor that creates longer wait times is the reliance on emergency rooms as primary care providers by patients who lack health insurance, have no regular care, or are mentally ill and have no other care available, an issue that makes up as many as 5% of ER visits.

Compounding the overcrowding crisis in certain areas is an epidemic of rural hospital and emergency room closures. Hundreds of rural ER's have closed in the last few decades, forced to shutter due to the costs of treating uninsured patients, while getting little or no reimbursement. 

While the expansion of Medicaid under the Affordable Care Act helped slow this trend, at least 80 rural hospitals have closed since 2010, and hundreds more are in danger, particularly in southern states that refused the expansion. The potential repeal of the ACA only compounds the danger these rural hospitals face. 

While hospitals are testing out a number of ways to reduce ER wait times and overcrowding, the most important thing a person can do to avoid a long ER wait time is to only go if it's absolutely necessary. 

The U.S. National Library of Medicine lists a host of conditions that require an ER visit  or a call 911 to ensure faster treatment. But it also lists some conditions that can be seen by urgent care, or even by a primary care doctor. These include common illnesses like colds, the flu, earaches, sore throats, migraines, and low-grade fevers; as well as minor injuries, burns or cuts. 

Finally, when in doubt about whether to go to the ER, you can call either your doctor's office or a nurse's hotline provided by your insurance company. If the call is off-hours, the office will likely have a doctor or nurse on-call 24 hours a day. You can describe your symptoms to them, and let them give advice on whether to go to to the ER or handle the problem a less time-consuming way.