Uploaded on 2015-05-20 by martinecarney

They have the effect of directing traffic bound across those barriers into "bottle necks" that limit city planners choices. ![bridges on the Allegheny river in Pittsburgh US][1] > "A 2006 study[2] 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 the 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" > > http://en.wikipedia.org/wiki/Bridges_of_Pittsburgh ![Bridges and a tunnel route an interstate highway past downtown Pittsburgh US at the forks of the Ohio River. ][2] [1]: https://edxuploads.s3.amazonaws.com/14321517881486725.jpg [2]: https://edxuploads.s3.amazonaws.com/1432151909736491.jpg