The massive evacuation effort in South Florida has millions fleeing Hurricane Irma

In preparation for Hurricane Irma’s assault on South Florida on Sunday, police are going door to door telling people to leave to avoid life-threatening rains, winds, and flooding. The mass exodus is creating large traffic jams on Interstates 95 and 75 and the Florida Turnpike, which can be seen on this live Florida traffic map.

Mandatory evacuation orders are in place for parts of Miami-Dade County, Broward County, Palm Beach County, Brevard County, and Monroe County. They affect nearly 650,000 people in the Miami-Dade county alone, and more than 1.3 million overall. (Thirteen counties are under mandatory or voluntary evacuation orders, according to BuzzFeed.)

The state’s various evacuation orders together make up one of the largest attempted mass evacuations ever. (Some are calling it the largest mass evacuation in US history.)

This is a gargantuan effort to get people out of harm’s way. But many are concerned about if and how the region’s residents will get to safety. The area also has unique demographics that make evacuation particularly difficult: 19.1 percent of the state’s population is 65 and older, the highest concentration in the nation, according to the Pew Research Center. (It’s not clear how many are in South Florida.)

Evacuating nursing homes is not a new thing for Florida. Florida requires each licensed nursing home, assisted living facility, and hospice to file a written plan with the Agency for Health Care Administration on how their patients will be evacuated if needed. Eleven hospitals had announced evacuations as of Thursday afternoon and about 140 health care facilities for the elderly have said they would evacuate, according to the Wall Street Journal. Thousands of inmates in state prisons have been evacuated too.

Elderly individuals living alone are at greater risk, but Florida counties do provide shelters for people with special needs including physical, mental, cognitive impairment, or sensory disabilities, and public busses have been used to transport the elderly to these shelters.

Another particularly at-risk group is the region’s homeless population. These individuals are being directed toward general population shelters, and those who refuse will be involuntarily committed to a psychiatric ward ahead of the storm, according to the Miami Herald. The Homeless Trust of Miami estimates there are 1,130 homeless people currently on the streets.

Unfortunately, as Vox’s Brian Resnick wrote, despite warnings, some people will never choose to evacuate their homes due to financial reasons, disabilities, or pure stubbornness.

The last major hurricane to hit the South Florida area was Hurricane Matthew in 2016, in which 1.5 million Floridians resided in mandatory evacuation zones. Matthew changed course last minute, mostly sparing Florida but wreaking havoc on parts of Georgia and South Carolina.

Irma is expected to cause catastrophic damage and has already been one for the record books, sustaining 185 mph winds for more than 24 hours, a record length of time for a hurricane in the Atlantic.

“I’ve been here 60 years. I’ve never heard of this kind of evacuation,” Miami-Dade Mayor Carlos Giménez told reporters.