The wait times at airport security checkpoints have become a guessing game during the shutdown of a single U.S. government department, with the daily attendance of Transportation Security Administration officers determining whether lines move quickly or stretch far outside terminals.

Travelers at Houston’s largest airport endured hourslong waits Thursday morning due to staffing issues, causing some to miss their flights or to have to scramble to their gates.

But at Atlanta’s Hartsfield-Jackson International Airport, which saw some of the country’s longest security lines on Wednesday, officials reported largely moderate-to-low wait times, though one checkpoint was closed due to low staffing.

Experts said it’s hard to predict where the lines will be the longest at any given time because much of the problem stems from TSA personnel not showing up for their shifts. The roughly 50,000 federal workers who screen passengers and bags have been working without pay while lawmakers fail to agree on funding the Department of Homeland Security .

The shutdown is the third affecting TSA workers since the fall. Growing financial strain makes it harder for them to afford basics, like gas or childcare, while continuing to report for work, according to the American Federation of Government Employees, the union that represents most airport security screeners. Homeland Security has said at least 366 TSA agents have quit since the current shutdown began on Feb. 14.

“This is a very unfortunate situation and an extreme situation, and one that has been dragging on far too long, and is only likely to get worse,” said Eric Rosen, director of travel content for the travel and finance site The Points Guy.

Rosen urged travelers to check security line wait times at their specific airport, either on the airport’s website or via its social media feeds. Some airports also specify which security checkpoints are open and closed, he said.

That’s useful information for the vast majority of travelers who are using the regular security lanes, he said. But given the current situation, programs that let people skip ahead can be hugely valuable. For example, when wait times hit three hours in Houston recently, getting through the TSA PreCheck line took 10 minutes, Rosen said.

“It can cut down wait times even during the best times when things are flowing smoothly, but right now we’re seeing the true value of that,” he said.

Another option for shortening wait times is Clear+, a paid membership that allows users to bypass the line for getting their identities and boarding passes verified and to move directly to bag screening. The company declined to say whether it has seen an increase in members in the last month.

But traveler Sara Oberton said Thursday that she and fellow Houston passengers at George Bush Intercontinental Airport’s Terminal E were all funneled into one line, regardless of whether they had Clear+ or TSA PreCheck. An airport spokesperson declined to confirm specifics, saying only that the number of available TSA screening lanes can vary based on staffing levels.

Oberton, a fashion blogger, said it took her three hours to get through the line, causing her to miss her flight to Los Angeles.

“It is pure insanity here in Houston,” she said in a video posted on social media.

Rosen, from The Points Guy, also had some advice for those who arrive at the airport hours before their flights but still find themselves in danger of missing them: Ask an airline representative if you can cut the line.

“I know it’s a little cringe and I know it’s a little uncomfortable,” he said. “But it’s not like showing up 20 minutes before your flight and expecting just to breeze through.”

That said, airlines aren’t required to help passengers who are stranded because of the TSA staffing woes.

“It’s not on them to make sure that you get to the gate on time,” he said.

R.j. Rico, Rio Yamat And Holly Ramer, The Associated Press