(AP)
TSA checkpoint lines at SeaTac Airport.

Airport security lines across the US have become unbearable, and checkpoints operated by the Transportation Security Administration have come under fire for their lengthy wait times.

According to the Port Authority of New York and New Jersey, the average maximum wait times at JFK International Airport's security lines have shot up 82% compared with 2015.

The TSA and its checkpoints have been around for a decade and a half.

So what has caused the sudden ballooning of wait times?

While it might be tempting to look for a single mistake on the part of the TSA, gridlock at America's airports was in fact caused by a confluence of factors.

1. The travel industry is booming

Air travel is growing a record pace. According to the International Air Transport Association, demand for air travel in North America increased 4.3% last year while domestic air travel in the US surged 5.5%.

Some airports have reported even higher figures. Hartsfield-Jackson Atlanta International Airport reported a 10% increase in traffic for 2015 and became the first airport to host more than 100 million passengers in a year. For the first quarter of this year, the world's busiest airport reported a 14% increase in travelers.

Chicago's O'Hare international reported a 10% increase in passengers, while Los Angeles International reported a 6% increase in 2015.

In other words, more people than ever are flying.

2. The TSA is grossly understaffed

While the number of people flying has surged, the number of security screeners has not. In fact, according to The New York Times' Ron Nixon, the number of TSA screeners have dropped 12% since 2011. In 2011 the TSA employed 47,630 screeners. By this year that number had fallen to 41,928.

The TSA blames this chronic understaffing on a series of cuts to its budget. In 2011 the agency operated with a $7.6 billion budget. In 2015, however, its fund had shrunk to roughly $7.3 billion.

To help alleviate the problem, Congress gave the TSA an additional $34 million in funding this month. Eight million dollars will go toward hiring 768 new screeners, while $26 million will pay for additional part-time hours and overtime.

But this may not be enough. The lack of available of workers has gotten so bad that major airports in Atlanta, New York City, Phoenix, and Charlotte, North Carolina, have threatened to bring in private-security contractors if the TSA is unable to improve its performance. In addition, Seattle-Tacoma International Airport in Seattle has already hired 90 private-security screeners to supplement the TSA.