WASHINGTON — The head of the U.S. Transportation Security Administration will retire after four and a half years leading the 60,000-employee agency, the Department of Homeland Security said on Thursday.

John Pistole, who has led TSA since June 2010, has overseen security operations at more than 450 airports around the United States, the department said.

Pistole “has been integral in leading TSA’s transformation to a risk-based, intelligence-driven counterterrorism agency dedicated to protecting our transportation systems,” Homeland Security Secretary Jeh Johnson said in a statement.

“Because of his efforts over the past four and a half years, our country’s transportation systems are more safe and secure,” Johnson added.