Thanksgiving signals one of the busiest travel periods of the year.

And even those signed up for the TSA’s Precheck program should expect extra company.

The TSA says more than 4 million travelers have joined the program nationwide, more than double the 1.8 million people enrolled at this time last year.

The program lets passengers skip general security lines and forego removing shoes, belts and other items. First they must apply online, pay a fee and undergo a background check in-person.

To help all lines move quickly, the TSA plans to fully staff Denver International Airport during the holiday rush. DIA will also assign workers to help with non-security tasks, like moving bins and managing lines.

More than 12 million people receive expedited screening in some form. While it’s too late to enroll in Precheck for Thanksgiving, you can get the process started in time for Christmas by visiting the TSA’s website.