After watching an episode of “Trains and Locomotives,” I began wondering what the difference was between a bridge, a trestle, and a viaduct. In the glossary of common terms found on this site, I learned only a bridge crosses water. In the show I watched, both trestles and viaducts were made of metal (steel?). How is it determined which is which?
I belive that a trestle, by definition, has vertical support throughout the span (essentially, legs everywhere). Thus, the old wood and steel bridges that looked like something put together with an erector set are trestles.
I also think that the term trestle gets used mistakenly a lot when refering to bridges that are really viaducts (or bridges).
Of course, I could be wrong.
Can a viaduct be a bridge? [%-)]
Again, people will call things whatever they call them, but a viaduct spans the depression created by a valley, while bridge generally goes over something smaller (like a river or a road). That being said, some rivers are wider than some valleys, and some viaducts go over rivers too, and there are a lot of bridges that have official names that include the word viaduct… so it’s not a clear answer.
To me, based on the definition… a viaduct is over a valley, unless it has little horizontal support and thus, is made up of a cluster of legs, in which case it’s a trestle… and everything else is a bridge… but it’s still ambigous.
A Viaduct by definition is a long elevated roadway, A bridge is a short roadway over a gap
or depression. It would seem a Viaduct may contain Bridges.
RABEL’s definition is probably about the best and keeps the fudge factor in mind. Using that definition, a trestle could be classified either way.
Thanks for the info. [:D]
My parents grew up in Chicago where every railroad bridge over a street is a “viaduct.” [:-^]
I was always under the impression trestles were wooden. I never thought they could be steel. [D)]
The Atlantic Avenue Viaduct in Brooklyn NY, by the way, is a very long steel structure, with legs at almost every ten/twenty feet and no valley anywhere near it.
Webster’s New World Dictionary describes a viaduct as a series of short concrete or masonary spans supported by piers or pylons meant to traverse a gorge or a valley. A secondary description is of any railroad bridge.
My own mental image of a viaduct is of concrete arched spans supported on piers across an expanse, and usually a road or a water course runs atop it. However, I have also seen images of long, high, “viaducts”, such as the huge one near Lethbridge, AB on the CPR line, which I would say was a steel trestle.
A trestle has battened stilt-like posts or bents to support wooden or steel spans. So, as much as there is a lot of room for area and industrial culture-specific use and cross-use, I will hold to a viaduct being something like a longish stone/masonary arch or pier-supported bridge comprising at least two spans, and a trestle being more supported by battened posts/bents, with the entire structure either wood or metal.
-Crandell
Why a duck? Why a no chicken?
------Chico Marx__, The Cocoanuts__, 1929.
It might depend on where you live. Around here, a viaduct goes over a road or rail line. A trestle goes over water-like a bridge, except with a lot of poles/posts for support.
Chicago is an exception to the “rule” , railroad Bridges pass over Viaducts.[:o)]
Chicago has many exceptions to all “rules!” [;)] You gotta problem wid dat?
M.S.- If I remember right, the show was about a UP line in the Pacific Northwest. They showed trains on all three.
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