Complex sentence: The Allegheny County, Pennsylvania Belt System is a unique system by which Pittsburgh and surrounding neighborhoods are looped by color-coded, streets that also retained their previous names, instead of the number-coded limited-access roads that surround most American cities.
Split into simpler sentences: The Allegheny County, Pennsylvania Belt System is a unique system of well-marked routes around the city of Pittsburgh. This is in contrast to the the number-coded limited-access roads that surround most American cities.