Patients at the Mission of Mercy free mobile medical clinic in the state of Maryland usually begin lining up before dawn just to get a shot at seeing the dentist or doctor.
Most haven't seen any kind of medical professional in months, many have run out of vital medicines for chronic conditions, and all have few other options to access any kind of healthcare.
According to a recent study by the non-profit organization Families USA, one out of three Americans spent a stretch of time last year with no medical coverage. Health insurance is out of reach to many in the United States because it is so expensive.
"Because of the troubled economy, people losing their jobs, we have seen a soar in patients," said Gianna Talone-Sullivan, the founder of the Catholic group which is funded solely by private donations.
The government covers medical costs for the poor and the elderly, and over half of Americans are covered by their employers. But many are stuck somewhere in between.
"A lot of people just fall right through the cracks," said Talone-Sullivan. "They make too much money to be on medical assistance but not enough to purchase healthcare."
Every other Monday morning, Talone-Sullivan's trailer packed with medical equipment pulls up to a church in Frederick, Maryland -- about 50 miles (80 kilometers) northwest of Washington, arguably the most powerful city in the world.
The group of volunteers and a handful of paid staff set up shop to provide health services, including dental care, physical therapy and pre-natal care, to about 150 people per day.
The bus also goes to eight other locations, and the larger organization has 650 volunteers working in five states.
Mobile and free clinics are common in underprivileged and rural areas of the country. Many are free, but some charge nominal fees on a sliding scale, depending on a person's income.
When Talone-Sullivan started the now extensive network of free clinics-on-wheels 15 years ago, she decided she would not take any government funding, because of the requirement that patients be treated only if they met maximum income requirements.
"We just don't want people to have to prove their poverty," she said fervently, insisting her organization's focus is to preserve patients' dignity and make sure Mission of Mercy never has to deny care.
Dora Andrade, a 25-year-old mother of two, was waiting anxiously for several hours in the make-shift registration area on a recent Monday.
For several years, she has suffered from nearly constant debilitating headaches. She works at McDonalds, and has no health insurance. Andrade began to worry the headaches could be something serious, and a friend suggested she come to the mobile clinic.
"If I were to go to a hospital," she said, laughing at the idea, "I would get a bill in the thousands. Not the hundreds, the thousands."
After spending several hours in the waiting area, Andrade finally boarded the cramped but cozy trailer that holds three tiny offices where volunteer doctors and Medical Director Michael Sullivan consult with patients.
"Breathe in," Sullivan told Andrade after she climbed on to the examination table. After several questions, and examining Andrade to make sure that she had no signs of swelling in the brain, he diagnosed her with migraines.
Andrade walked out of the trailer with a prescription for two kinds of medications that Mission of Mercy will fill for free, and for a brain scan.
Thanks to a deal between the clinic and the local hospital she can also go get the scan without having to worry about the bill.
But Sullivan warned that despite their success, finding funders is one of the toughest parts of running a free mobile clinic like Mission of Mercy. And they are not an answer in addressing the healthcare crisis in the US.
"I don't think we've created a model that could be replicated everywhere and serve the need. The needs are too great," he said.
The people who come here, he explained, often suffer from preventable problems or conditions that have gone untreated because patients had nowhere else to go.