What is a Bridge? Part II

When I wrote the first “What is a Bridge?” post, I felt confident that Merriam-Webster’s definition of a bridge, “a structure carrying a pathway or roadway over a depression or obstacle,” was sufficiently explicit to exclude ramps.  However, while crossing the Penn Ave Bridge in East Liberty I found a new structure to challenge the definition of a bridge.  The former bus ramp from the former Penn Ave (Bus) Station to the (not former) East Liberty Busway Station meets the above definition of a bridge as it carries a roadway over the obstacle presented by the railroad bordering the Busway.  On the other hand it also meets the definition of a ramp, “a slope or inclined plane for joining two different levels,” as the Busway is significantly lower than most of the surrounding area.  So is it a bridge or a ramp?  It almost feels like asking is a tomato a fruit or vegetable? or perhaps even which came first, the chicken or the egg?  Are these equally impossible questions to answer or is it rather the case that there are exceptions to every rule?  There aren’t always easy or straight-forward answers.  I suppose in this case the structure is both a bridge and a ramp.

Perhaps a way to answer the question a little more specifically is to look at the way it is used.  In its previous use, the point of the structure was to get buses down onto or up out of the lower Busway level.  While it was used in this fashion, I’d say it was more a ramp than a bus.  There is a future plan for it to be turned into a pedestrian bridge to transport pedestrians safely across the railroad and Busway to the Busway station (see Busway Bridges: East Liberty post for more information).  At that point, in function the structure will be more of a bridge, though I suppose the ramp end will still function as a ramp to provide more accessible access to the station than stairs.  Whether it is a ramp or a bridge, I did not walk it yet as it is not currently designed for pedestrian access.  After its conversion is complete in the next couple years, I will come back to walk it.

To return to the Penn Ave Bridge, which is the one I did walk, as you travel west on the Busway from its beginning in Swissvale, the Penn Ave Bridge is the first of many to cross the Busway within the borders of the City of Pittsburgh.  According to a book I read recently, the valley that the Busway and the parallel railway travel through was created before the last Ice Age.  Before that time, the book explained, the Monongahela River (the “Mon”) traveled north to the region that is now Lake Erie and this valley was its route; however the ice flows during the Ice Age diverted the river into its current path toward the west where it meets the Allegheny to form the Ohio River.  The valley formed from the former riverbed of the Mon contributes to Pittsburgh’s hilly landscape and its high bridge count.  See the Taking the Long Way Round post, Busway Bridges: East Liberty post and more future posts with the header “Busway Bridges” for more on these bridges.


4 thoughts on “What is a Bridge? Part II

  1. Pingback: Busway Bridges: East Liberty | urbantraipsing

  2. Pingback: What is a Bridge? | urbantraipsing

  3. Pingback: Busway Bridges: Millvale Avenue | urbantraipsing

  4. Pingback: What is a Bridge? Chicago Edition | urbantraipsing

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