The difficulties are particularly acute for visitors departing through land exits, said Richard Stana, director of homeland security issues at the Government Accountability Office. "Interstate highways may have to be rerouted" to verify land exits, he said.
The effort is part of the US VISIT program to track entrances and exits to the United States -- the latter of which have proved more difficult. At land exits, the process of verifying biometric data has the potential to create major traffic backups.
Stana said airports and seaports likely have sufficient infrastructure in place to track departures.
Robert Mocny, who serves as US VISIT's acting director, told the committee that DHS will be ready to verify exits by air and sea this year. But it could take up to five years to install biometric traveler exit verification equipment at land ports, he said.
"We're going to wait for the technology to catch up to us," Mocny said. "The exit portion is something we have to work on." There is no target date for when that part of the program will be finished.
According to Stana, the ground-based exit verification component of the US VISIT program is nowhere near completion. Of the pilot programs the agency has conducted, "none… was particularly effective," he said.
Mocny emphasized that many phases of the program have been completed.
But lawmakers were still critical.
Rep. Bennie Thompson, D-Miss., chairman of the committee, said US VISIT directors "shifted… the intent of the program" and "lowered the status." He also expressed disapproval that the program has only an acting director.
"You need to put people in place to get the job done," Thompson said.