The Philadelphia Main Line, known simply as the Main Line, is an informally delineated historical and social region of suburban Philadelphia, Pennsylvania. Lying along the former Pennsylvania Railroad's once prestigious Main Line, it runs northwest from Center City Philadelphia parallel to Philadelphia and Lancaster Turnpike, also known as U.S. …The Philadelphia Main Line, known simply as the Main Line, is an informally delineated historical and social region of suburban Philadelphia, Pennsylvania. Lying along the former Pennsylvania Railroad's once prestigious Main Line, it runs northwest from Center City Philadelphia parallel to Philadelphia and Lancaster Turnpike, also known as U.S. Route 30.