Homeland Security Secretary Jeh Johnson has directed Customs and Border Protection (CBP) to implement a biometric exit solution at U.S. airports beginning in 2018, making use of new visa fees enabled by Congress in the federal spending bill for FY ’16.

CBP has already begun testing technologies for a biometric exit system for nationwide deployment, Johnson says in his annual State of Homeland Security address earlier this month at the Woodrow Wilson Center. He says the omnibus spending bill approved by Congress authorizes $1 billion in fee increases over 10 years to pay for the implementation of a biometric exit system, leading him to direct CBP to begin implementing the system at U.S. airports in 2018.

In 2015 CBP began testing the use of mobile systems to capture the fingerprints of departing foreign nationals on some flights at 10 U.S. international airports. The BE-Mobile testing is expected to last until this summer and so far has been deemed positive by the agency but still too expensive for nationwide deployment. CBP officials believe a mobile fingerprint-based biometric exit system might be better suited for small and mid-size airports where there are fewer departing international flights.

Last year the agency also conducted testing of face recognition technology at Dulles International Airport near Washington, D.C., and in January rolled the technology out to John F. Kennedy International Airport in New York. The face recognition system is being used to screen select passengers arriving on international flights and will be rolled out to additional airports throughout the year.

Later in 2016 CBP plans to begin a new pilot program that captures face and iris images to help verify the departure of foreign nationals from the United States. One of CBP’s paramount concerns with any biometric exit solution is that it be deployed in an area to ensure that once a person’s biometrics have been captured, that that person boards his or her flight and is not able to simply turn about face and leave the airport through the front door.

In December CBP also began testing face and iris image capture capabilities for certain foreign nationals arriving and departing the United States at the Otay Mesa land port of entry in California. This testing, which is ongoing, is aimed at helping CBP understand how to implement a biometric exit system in the land environment.

Congress in 2004 began mandating that DHS deploy a biometric exit solution for foreign nationals departing the United States to better identify foreigners who have overstayed their visas.