GAITHERSBURG, Md. -- Police escorted a procession of trucks hauling steel from the World Trade Center towers out of the area Tuesday morning.

For the past three years, the steel had been at the National Institute of Standards and Technology, where the events of the Sept. 11, 2001, terrorist attacks were reconstructed. The steel is being taken back to New York City.

NIST and its contractors and collaborators recommended "action in the areas of increased structural integrity, enhanced fire endurance of structures, new methods for fire resistant design of structures, enhanced active fire protection, improved building evacuation, improved emergency response, improved procedures and practices, and education and training."

The convoy traveled down Interstate 270 to the Beltway, then north on Interstate 95 toward New York.

Every truck was flying the Star-Spangled Banner, NBC4 viewer Heather Salley said in an e-mail.

"Very sobering drive to work," she wrote.