The part of U.S. Interstate 76 (formerly I-80S) that runs from Exit 24 of the Pennsylvania Turnpike at Valley Forge to Passyunk Avenue in Philadelphia. Often called "Surekill Expressway", referring to its safety (or lack thereof). Its construction predates the signing of the National Highway System bill, and it's evident in its design.
Its history, some interesting facts, and more, can be found at the Pennsylvania Highways page at http://www.pahighways.com/IHwys/I76.html.