The summer I spent walking Pittsburgh bridges, I complained about the cages on the Millvale Avenue Bridge, the Highland Park Bridge, and the Graham Street pedestrian bridge. The narrow sidewalk and chain link fences on the first two examples and the chain link cage on the third example made me feel yucky and claustrophobic. Thanks to one of my blog followers, I recently learned that people tend to throw things onto moving objects, which is why bridges like the Millvale bridge have higher fencing along portions over roads and railroads. I still wished there was a cage-free option to meet the same goals of the bridge builders.
In Bethlehem, PA, I found just such an option on the Fahy Bridge. It is a fairly plain concrete bridge saved from the ugliness and gloom of many concrete bridges by using a functional, yet decorative, railing instead of the more common functional, yet ugly, chain link fence. This railing was installed during the 2016-18 renovation of the Fahy Bridge. Recent bridge renovations and replacements in Pittsburgh also feature more decorative railings. While the first of these new bridges in Pittsburgh tried to dress-up a chain link fence cage, the later ones are successful cage-free bridges even when they incorporate chain link fencing.* These examples give me hope that the days of caged bridges may be a thing of the past.
*Note: I have a to-do item to go back and photograph these new bridges for future posts, but no set timeline for the completion of this task.
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.
I’ve walked numerous bridges and yet I didn’t try building a bridge until my fifth Architectural Dessert Masterpiece. After the near disaster of the skyscraper, this one succeeded beyond my best hopes. With a deck made of shortbread, piers of pretzels, and a non-structural suspension system of wafers and Twizzlers, this one was so structurally sound that it was a challenge to split it into serving pieces.
The first place to show me how a city can be stacked like a layer cake, Chicago provided ample opportunities to explore all levels of the city. The experience of noticing the expansion joints in roads that I assumed were on solid ground opened my eyes to the possibilities of stacking uses.
Underground Life
A vacant lot two stories below street level solved the mystery of the expansion joints, by exposing the inner guts. Two more roads sit below street level to segregate trash pick-up and deliveries from the flow of traffic. These lover levels also provide some opportunities for parking without monopolizing valuable real estate above. Retail shops connected by pedestrian passageways are also interspersed in these layers.
River Life
At the same elevation as the “underground life,” the Chicago River flows through the heart of the city. On and along the river are a variety of activities. Pedestrian paths, cafes, housing, parks, industrial uses, and homeless encampments line the shores. Meanwhile, the river abounds with ducks, boat tours, water taxis, construction staging, and marinas.
Street Level
Back up on the street level, life buzzes. Vehicular and pedestrian traffic rush passed, occasionally pealing off to visit the numerous shops, offices, museums, restaurants, cafes, parks, and trails.
Pie in the Sky
Yet, more life looms above. Several of the skyscrapers have penthouse, or nearly penthouse, restaurants. Others have rooftop observation platforms. Between these and the street are many other opportunities for enjoying life including a religious sanctuary, the “L”, gardens, art, pedestrian bridges, and of course, offices, apartments, hotel rooms, and shops.
Unlike Pittsburgh, in Chicago, the public is welcome in some form on every level to gain a full experience of the city.
I mentioned previously that I totally geek out over maps. I recently came across a fascinating “new” map called The “Z” Atlas & Map of Pittsburgh, PA, and Mount Oliver, PA. I am adding it to the Sanborn Maps and GM Hopkins Maps as a go-to for studying the changes Pittsburgh went through in the 20th Century. The “Z” Atlas was published in 1952. There are two things about this map that caught my eye as setting it apart from others during my initial perusal.
First, in the street index, it identifies which streets have unusual addressing. Pittsburgh is known for some unique addressing situations. For example, there is a block where houses built before WWII have 1300 numbers and the ones built after WWII have 1400 numbers, even though they are intermixed. This atlas shows that the post WWII houses were built after 1952 because the address numbers on that street weren’t wonky yet.
Second, this map claims that “Pittsburgh has more streets than any City in the World. You will find EVERY ONE of them in this ‘Z’ Atlas and Map!”
“Preposterous,” I said, when I first read that claim. Pittsburgh’s land area is small compared to other large metropoles. It does not make Wikipedia’s current list of the 150 largest US cities by land area. Without digging into census data, I assume that many of the old cities (ex. New York City, Chicago, Cleveland), if not most of the 150 listed, likely were of a similar size in the 1950s as today. How could it be possible for Pittsburgh to have more streets than these cities that are significantly larger?
Pittsburgh’s many hills, ravines, cliffs, and rivers mean there are few long streets and many short streets. Maybe after all, Pittsburgh did have more streets than any other City in the World in 1952. Reading more of the “Z” Atlas, it elsewhere explains that Pittsburgh had over 6,000 streets at the time of the map’s publication. That number does include the numerous “paper” streets that were surveyed and mapped, “but never built or even marked in the dirt.”
Many of these paper streets still exist today causing headaches for the City and its citizens, but some have been vacated and turned over to private ownership. Between that and the rise of mega-cities since the 1950s, I won’t say that Pittsburgh can still claim more streets than any other city. A quick Google search showed that the question of what city has the most number of streets is not as well discussed as what city has the most bridges. Perhaps a more ambitious person than myself could run an analysis to see whether Pittsburgh still has more streets than any other City in the World. (Don’t forget to count the step streets!)
Last summer’s search for Roebling bridges (see Market St, Steubenville and Wheeling Suspension Bridge) came to a successful end as a golden sunset spread over Cincinnati. The reason we struck out earlier in the day is that the Cincinnati-Covington Bridge is one of the two remaining Roebling suspension bridges. The other is, of course, his most famous bridge: the Brooklyn Bridge. The first of Roebling’s five suspension bridges was built in Pittsburgh at the site of the current Smithfield Street Bridge, but lasted less than 40 years before the increased river and road traffic made it obsolete.
Between Roebling’s two remaining bridges, I found the Cincinnati bridge more appealing. Its character feels like it would fit right in on the Thames in London. I also appreciated the engaging green spaces at either end. The birds liked this bridge, too.
urbantraipsing 