What is a Bridge? Chicago Edition II

While poking around the map collection at Chicago’s Public Library, I discovered that the structures carrying roads over the railroad tracks in Grant Park are considered viaducts. The word viaduct brings to my mind a Roman structure soaring over a valley floor and conveying a flat road on top of towering stone arches. The Chicago “viaducts” do not fit that image. To me, they look like bridges with no striking difference between them and Chicago’s river bridges other than color and style of ornamentation. Both groups of structures have fairly flat roadbeds supported by piers. I am puzzled why one set of structures is called bridges and the other viaducts.

The main difference seems to be that the bridges are crossing a body of water while the viaducts are crossing an obstacle on land. This doesn’t feel like the answer, though. I’ve walked over 50 bridges in Pittsburgh, the majority of which are over land. Not one of these structures is called a viaduct. To help find clues to solve this puzzle, I looked up the definitions of bridge and viaduct.

Merriam-Webster’s definitions are not much help:

Viaduct: a long elevated roadway usually consisting of a series of short spans supported by arches, piers, or columns

Bridge: a structure carrying a pathway or roadway over a depression or obstacle

The Oxford English Dictionary has similar definitions:

Viaduct: an elevated structure consisting of a series of arches or spans, by means of which a railroad or road is carried over a valley, road, river, or marshy low-lying ground

Bridge: a structure forming or carrying a road, path, or (in later use) a railroad, etc., which spans a body of water, a roadway, a valley, or some other obstacle or gap, and allows a person or vehicle to pass unimpeded over or across it

Based on these definitions, the features that seem to distinguish a viaduct from a bridge are elevation and short spans. This still doesn’t help solve the question of why the Grant Park structures are viaducts and the Chicago River structures are bridges.

Next, I turned to “How to Read Bridges” by Edward Denison and Ian Stewart. The glossary defines viaduct as “a type of bridge over land formed by a series of small (usually arched) spans.” This definition seems to work best for the viaducts in Chicago. They are over land and have a series of spans, though the spans are not arched.

To further develop my understanding, I paged through the nine examples of viaducts in “How to Read Bridges.” All nine examples are elevated (such as the 330-foot high Goltzsch Viaduct and the 407-foot high Garabit Viaduct) and have multiple arches or piers (such as the 21-arch Glenfinnan Viaduct, the 8-arch Wharncliffe Viaduct, and the 5-pier Busseau Sur Grusse Viaduct). All, but one, have no support system above the road deck. The exception is the Millau Viaduct, which uses a cable-stayed deck on top of seven piers that range from 253 feet to 800 feet tall. All, but one, are over land. The Garabit Viaduct spans the Truyère Valley and one-third of its length crosses the Truyère River. In another example, the approaches to the Cubzac-les-Ponts over the River Dordogne are considered viaducts, but it is a bridge that crosses the river.

I find myself again at a loss. While the definition in this book seems to work for the Chicago viaducts, the examples do not look like the Chicago structures. To help the Chicago viaducts fit in, I propose a new definition built from the three definitions and nine examples above:

Viaduct: an elevated roadway, supported by many arches or piers over land.

Yet, there are exceptions to every rule. The nine examples in “How to Read Bridges” include exceptions to the support system of the viaduct and to the obstacle spanned by a viaduct. Expanding upon this, the Chicago viaducts, which are supported by multiple piers over land, become the exception to the elevated part of the rule or definition.

My biggest take away is that it is no easier to define a viaduct than it is to define a bridge. In most cases, as with bridges, a viaduct is something you know when you see it, even if you cannot define it. However, sometimes it takes a label or a sign, such as the maps of Chicago’s viaducts and, prior to its restoration, the maps of Heth’s Run Bridge, to know what you are seeing.


Other posts in this series:

What is a Bridge? Pittsburgh Edition I (July 18, 2012)

What is a Bridge? Pittsburgh Edition II (July 27, 2012)

What is a Bridge? Chicago Edition I (April 18, 2013)

What is a Bridge? Bethlehem Edition I (July 1, 2020)

What is a Bridge? Bethlehem Edition II (July 15, 2020)

17 thoughts on “What is a Bridge? Chicago Edition II

  1. According to my trusty Barnhart’s Concise Dictionary of Etymology, “bridge” is the much older term, going back at least to the old English “brycg” in use around 750. “Viaduct” doesn’t appear until 1816. I wonder what happened 204 years ago to inspire the new term.

    • …I wonder whether the connection to railroads might be important to the form. Trains can’t handle steep inclines and frequent grade changes navigable by smaller vehicles, so long structures to straighten the path would be necessary. The 1816 timing kinda fits, and I think predates structural steel, so a series of stone arches would be almost inevitable.

  2. Evidently the 1816 date comes from the writings of an English landscape designer, posthumously collected and published as “The Landscape Gardening and Landscape Architecture Of The Late Humphrey Repton, Esq.”

    ‘Viaduct’ appears on pp. 349, and 543-545. Rather than something different from a bridge, it’s a specific type of bridge aspiring to both utility and strength in contrast to what he felt were unnecessarily high and dangerous non-viaduct bridges. If it’s any consolation, the paragraph proposing the term concludes with an acknowledgement of the fuzziness of the term: “I have suggested, for several places, what may more properly be called a viaduct than a bridge, of which no idea can be given by description only.”

    Sadly, nothing to do with trains.

    • Thank you for digging deeper into this question! The quote from Mr. Repton that I came across as crediting him for coining the term was “I have ventured to suggest a hint for such a structure as may support the road…, rather calling it a via-duct than a bridge.” I think this came from the same source as your quote. I find both quotes interesting. The emphasis on the two components that make up the word (via=by way of and duct=act of leading or to lead) add to the confusion of the definition by suggesting it means by way of leading, which seems a circular conundrum. However, in your quote, Mr. Repton acknowledges that even in coining the term there was no way to clearly define it through a description.

      • Yes, I ran across your quote in that same text. FWIW, Barnhart’s indicates the source of the ‘via-‘ is the Latin for ‘road,’ which makes it less circular, though still just as murky. I got the impression that Repton was vaguely gesturing at a something he hadn’t really gotten clear in his own head. Another attribute he mentions is that a viaduct is primarily meant to facilitate passage over something, when there’s not need to also allow passage underneath.

        Your quote comes on page 545 where he’s describing a specific structure proposed for the grounds of Woburn Abbey: an attractive way to allow passage over a low earthen dam that was (or might’ve been) itself built only for the purpose of widening a stream to provide a sort of reflecting pool. The visual role of a viaduct in the context of a thoroughly designed setting seems to have been very important to the idea he meant to convey.

  3. Far afield from your original topic, but Repton was mentioned in a recent economics-themed podcast that interviewed an author about her very non-traditional management of the grounds at the Knepp Castle Estate. She remarked that it had been a “Repton park,” though Repton’s direct involvement is questionable. It was an offhand mention that would’ve been meaningless to me if not for wondering about bridges and viaducts.

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

  5. Pingback: What is a Bridge? Bethlehem Edition II | urbantraipsing

  6. Pingback: Chicago Waterfront I | urbantraipsing

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

  8. Pingback: What is a Bridge? Pittsburgh Edition II | urbantraipsing

  9. Pingback: What is a Bridge? Pittsburgh Edition I | urbantraipsing

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s