Running along First Street, the utility corridors passed over the Washington Terminal Company's railroad tunnel and under the Library of Congress book tunnel. The dimensions were cramped and swampy: tunnel workers shared the 7 foot tall, 4.5 foot wide space with steam pipes that raised temperatures over 100 degrees.

The steam tunnels were later expanded to the north to link up with Union Station, the Government Printing Office, and the old Post Office.

Construction on top of the First Street railroad tunnel was problematic, and in 1949 the Washington Post wrote that "vibration from the trains below, and traffic above, has caused the tunnel to settle unevenly from 18 to 24 inches."