The Scoop:
	I started this page after completing a page for Detroit that covered the 
	majority of bridges and overpasses found in the metro area.  This is an 
	introduction to the many varieties of railroad bridges that exist, and some 
	that are no longer with us.  For further reading, check out some of the 
	links I have come across.
	
	Bridge - Overpass - Viaduct.... What is the difference?  The large 
	majority of the bridges mentioned below can probably be referred to as a 
	bridge or an overpass, and the terms are interchangeable.  One fellow 
	who helped me with another page in PA is a "bridge guy", and may disagree.  
	Being that almost all bridges in 
	Detroit are "older", I don't think any 
	qualify as being called a viaduct, but some, like #8 and #9 going to Zug 
	Island, are bridges, and not overpasses or viaducts.  I reference this 
	page in Detroit, because, as I said, this is what got me going on this page.
	
	A viaduct is a specific type of bridge that consists of a series of arches, 
	piers or columns supporting a long elevated railway or road.  Typically 
	a viaduct connects two points of roughly equal elevation, allowing direct 
	overpass across a wide valley, road, river, or other low-lying terrain 
	features and obstacles.
	
	Acknowledgements:
	Structsource
	Google Maps
	Open Railway Maps
	Bing Maps
	Denver Todd
	Dave Frieder
	Scott Dunn
	Adam J.W.C
	Bob Castle
	Rich W.
Websites and other additional information sources of interest for the area:
	
	http://www.structsource.com/railroadbridge/main.html 
	
	https://en.wikipedia.org/wiki/Viaduct 
	
	http://pghbridges.com/termsBrg.htm 
	http://pghbridges.com/basics.htm 
	covers railroad and automobile bridges, extensive descriptions, but no 
	pictures or diagrams to help explain
	
	
	
	
	Bridge Types
	
	FIXED BRIDGES
	Steel Girder
	Steel Truss
	Precast Concrete
	Trussed Through Arch
	
	MOVABLE BRIDGES
	ABT Bascule
	Lift
	Swing
	
	Here is one listing of railroad bridge types, however, it is for "modern" 
	bridges being built today, and doesn't include a lot of the "older" ones 
	found around any town of reasonable "old" age, like Baltimore, Detroit, and 
	Chicago.
	
	 Stuff in grey is from Strucsource
 
	Stuff in grey is from Strucsource
	
	 From pghbridges.com
 From pghbridges.com
	
	
	
	FIXED BRIDGES
	
	Trestle's
	Trestle Type Bridges
	
	
	
	Steel Girder Types
	Steel Deck Girder
	 
 
	
	
	Steel Open Deck Girder
	 
 
	
	
	Steel Through Girder
	 
 
	
	
	Steel Truss
	Steel Through Truss
	 
 
	
	
	Bollman Iron Truss
	GPS Coordinates: 39.13485, -76.82506
	This is the only surviving example of this type of bridge, built by the B&O in 1852, 
	and moved to Savage MD in 1887.
	I have a whole page dedicated to this bridge here.
	
	
	
	Precast Concrete
	Precast Concrete Double Box Girder
	
	
	Precast Concrete Box Girder
	 
 
	
	
	Precast Concrete I-Beam Girder
	 
 
	
	
	CIP Concrete Trough
	 
 
	
	Precast Concrete Slab Girder
	
	
	Prestressed Concrete Box Girder
	 
 
	
	
	Trussed Through Arch
	
	Hell Gate Bridge
	GPS Coordinates: 40.78269, -73.92219
	https://railfanguides.us/ny/NYChellgate/index.htm
	
	https://en.wikipedia.org/wiki/Hell_Gate_Bridge
	
	
	https://en.wikipedia.org/wiki/Sydney_Harbour_Bridge
	
	
	https://en.wikipedia.org/wiki/Tyne_Bridge 
	A bridge (almost) in a class all of it's own.  I used to sit up at night in the 
	60's and watch the New Haven trains come and go over this bridge.  
	Priceless memories!!!
	Hell Gate is not the largest, but it was the first, completed in 1916.  
	It is 1,017 feet long, but 17,000 feet if you include the elevated 
	approaches, and clears the water below by 135 feet.  It goes between 
	the Queens and the Bronx via Ward and Randall Islands.  It was built by 
	the New Haven RR.
	
	Sydney Australia has the largest of these: the Sydney Harbour Bridge - it 
	carries car, rail, and pedestrian traffic, and you can even climb to the top 
	of it!  It was completed in 1932, and Hell Gate did provide the 
	inspiration for using this type.  It is 1,149ft long, and sits 161 feet 
	above the water.  It carries 8 car lanes and 2 streetcar tracks 
	electrified at 1,500 volts.