<P> The Bridges of Pittsburgh play an important role in the city's transportation system . Without bridges, the Pittsburgh region would be a series of fragmented valleys, hillsides, river plains, and isolated communities . </P> <P> A 2006 study determined that Pittsburgh has 446 bridges, and with its proximity to three major rivers and countless hills and ravines, Pittsburgh is known as "The City of Bridges". The city of Pittsburgh and Allegheny County are the largest owners of great bridges in the country, in proper proportion to their size, with the possible exception of the City of New York, which is built on an island and surrounded by large bodies of water . </P> <P> According to a 2011 study by Transportation for America, 1,194 bridges in the Pittsburgh area--or 30.4%--were deficient, the highest proportion in the nation . </P>

How many bridges in the city of pittsburgh