If you’ve grown accustomed to being waved through the PreCheck security lanes at the airport without having paid to enroll in the popular program, time is running out.

The program has been so successful that the Transportation Security Agency plans to limit it soon to those who enroll — and pay up.

TSA administrator John S. Pistole, explained the change recently.

Of all domestic air travelers, “now we’re around 45 percent” for those receiving PreCheck screening, said Pistole.

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With the PreCheck program on solid footing, Pistole said, “We’ll start pulling back on the number of people who we include on a random, managed-inclusion basis, because we want to, frankly, cater to those who have actually signed up, and who we have the highest confidence in because we know the most about them.”

About 440,000 people have paid to enroll in the PreCheck program, which provides a quick pass through special airport-security checkpoints (including at Sea-Tac Airport). Travelers using PreCheck do not need to take off shoes or light outerwear, and are not required to remove laptops or liquids in the prescribed amounts from carry-on bags.

In the last year, many travelers who have not enrolled have been happy, but in many cases baffled, by being sent into PreCheck lanes available at 118 airports. That is because the agency set a goal of putting 25 percent of domestic travelers through the quick-pass lanes by the end of 2013.

But as enrollment centers geared up slowly last year, the agency decided to increase the numbers by giving PreCheck passage randomly to many other, nonenrolled travelers whose profiles — as kept in the Secure Flight databases compiled by airlines and the agency — indicated they were low-risk.

One unintended consequence of sending uninitiated travelers into the PreCheck lanes was confusion. Frequent travelers who belonged to PreCheck or other trusted-traveler programs grumbled that PreCheck lanes on many occasions became clogged with bewildered passengers who held up lines by removing their shoes and jackets and behaving just as they have been conditioned to behave at regular checkpoint lanes.

Pistole said that while the agency had made some gains, there was work to do. “I would say there’s still some confusion, but not nearly what it was when we first introduced what we called managed inclusion,” Pistole said, referring to the random inclusion of those not enrolled.

Now that it plans to phase out that group, the agency is looking to form partnerships with private vendors “who can help us increase PreCheck enrollment, which will then result in us having more and more lanes devoted to PreCheck,” Pistole said.

It costs $85 to enroll in PreCheck for a five-year period. Applications can be made online (see tsa.gov/tsa-precheck). A visit is then scheduled at an enrollment center (now at 26 airports and hundreds of other federal offices, including in the Seattle area), where the applicant provides identification, basic personal information and fingerprints. Once approved, the traveler gets a Known Traveler Number, which is entered in that person’s airline profile or each time a flight is booked.