U.S. Customs and Border Protection has processed approximately 35,000 passengers through a test version of a new system designed to combat visa overstays, the agency’s deputy executive assistant commissioner John Wagner told a House subcommittee last week.

Customs and Border Protection has been developing a biometric entry-exit tracking system since fiscal year 2013. President Donald Trump issued an executive order Jan. 27 pressing on DHS to expedite the completion of the system.

The test demonstration, which has been in place at the Atlanta Hartsfield International Airport since June 2016, involves taking a foreigner’s photograph before the flight and storing it in a database to track people entering and exiting the country using a visa. This provides a platform to track which temporary visa holders have overstayed their legally allowed time in the United States and accelerate the process of removing them.

Wagner said CBP is expanding its test demonstrations to Chicago O’Hare International Airport, Houston George Bush Intercontinental Airport, Washington Dulles International Airport, “plus four additional large airports.”

“Most overstays bank on the fact that no one would even be looking for them because of lax enforcement and no real system to identify people who overstay their visa,” Sen. John Cornyn said during his opening remarks. “In 2016 alone, more than 700,000 aliens stayed in the US past their authorized time.”

Moving forward, the hearing calls for the project to expand its scope to include seaports and land ports in addition to airports. “We have no way of determining when people exit, especially when they exit through land ports” says Senator John Cornyn.

The project also seeks permission to require Visa Waiver Program visitors to undergo similar biometric requirements — a program that admits more than 20 million people into the U.S. on a temporary basis every year.

Attorney General Jeff Sessions has made it clear that visa overstays will be an administrative priority since many homeland security threats, including 9/11 and the shoe bombing, were carried out by such overstays.

“We have to have a complete and effective biometric (facial recognition) exit system in place, no matter how people come and go, including sea and land ports of entry,” Cornyn said.