WASHINGTON — Significant progress has been made on shortening screening lines since earlier this spring when airlines reported thousands of frustrated passengers were missing flights, the head of the Transportation Security Administration said Tuesday.

Over the busy Memorial Day weekend, 99 percent of passengers at U.S. airports waited less than 30 minutes and 93 percent waited less than 15 minutes in regular security lines, Peter Neffenger told a hearing of the Senate Homeland Security and Governmental Affairs Committee. In TSA Precheck lines for travelers who have received priority security vetting, 93 percent of passengers waited less than 5 minutes, he said.

The agency said it is reducing lines partly by adding more lanes and increasing staffing at peak periods, especially at seven of the nation’s busiest airports: John F. Kennedy in New York, Newark in New Jersey, O’Hare in Chicago, Miami, Atlanta, Dallas-Fort Worth and Los Angeles.

“When you get stories of long wait times it has primarily been those airports,” Neffenger said. “If you can prevent problems from happening there, you don’t have problems that cascade throughout the system.”

TSA also is exploring the possibility of adding automated screening technology at more than a dozen airports that can speed up lines by as much as 30 percent, he said. After TSA viewed the technology in operation at busy Heathrow Airport in London, Delta Air Lines helped pay for its installation two months ago in two screening lanes in Atlanta, he said. The new system has been such a success that other airlines and airports have contacted TSA about installing the systems, he said.