Today’s Wonder of the Day was inspired by Jada. Jada Wonders, “How do people make bridges?” Thanks for WONDERing with us, Jada!
Are you a fan of the Harry Potter books and movies? If so, you've probably dreamed at one time or another of boarding that magical train that winds through the countryside to bring you to the school of your dreams, Hogwarts.
Depending upon where you live, your view of trains might differ from that of others. Those in small, rural communities often see trains as a means of moving heavy commodities, such as coal, from one place to another.
Those living in large cities, on the other hand, probably think of trains as an economic and efficient way of transporting people from suburbs to the city. Some large cities even have a vast system of underground trains that move people throughout the city.
Wherever trains go, they occasionally need to pass through areas with deep valleys or gorges or busy city streets. Engineers solved this problem long ago by inventing a unique structure that would carry traffic across these obstacles.
Sounds like a bridge, right? Well, it is…sort of. Roman engineers called them viaducts, and the first ones were built in a similar way to the aqueducts that the Romans made famous.
You'll hear different terminology used from time to time. Some people refer to these structures as viaducts, while others may call them railroad bridges. To be technical, all viaducts are indeed bridges, but all bridges aren't necessarily viaducts.
So what's the difference? Some people point out that viaducts mainly carry a railroad or a road over a gorge, valley, or busy intersection, while bridges are mainly built over water. Viaducts can and do pass over water occasionally, though.
The key differences can be found in their construction. Viaducts usually consist of a series of multiple bridges connected by a series of arch structures or spans between tall towers made of stone, concrete, iron, or steel.
Viaducts usually connect two points of terrain similar in height for the purpose of carrying rail or automobile traffic across a valley, gorge, canyon, or street traffic. Their construction and design tends to be simpler and cheaper than that of bridges.
Bridges make use of a wide variety of designs and materials. Compared to viaducts, bridges are usually longer and more expensive to build. One way to try to differentiate the two is to look for intermediate arches or supports. Viaducts usually have several while bridges might not have any.
In large cities, rail viaducts create spaces at street level between their spans. These spaces can often be used for parking or commercial buildings. Viaducts aren't used as often to cross bodies of water, because the supporting spans usually aren't very wide, which limits the type and size of boat traffic that can travel below.