Can you imagine being an early explorer? Setting out to discover new lands, you couldn’t predict what you would find. Sooner or later, you would surely run into rivers or other bodies of water that you would have to cross to continue your journey.

Early settlers who chose to make a home in a new area often had to decide where to live based upon the location of rivers and streams. Not only were these waterways sources of water, they also enabled settlers to travel to other areas.

To make travel between settlements separated by bodies of water easier, bridges were eventually built. Today, we take them for granted. But think about how much more difficult life might be if they didn’t exist!

The first bridges were most likely simple logs placed over small streams. The science of engineering has come a long way since then. Now, bridges of many types are used to make it easier to cross over a variety of obstacles, including waterways, valleys, roads, and railroad tracks.

Believe it or not, there are over 500,000 bridges in the United States today. They come in a variety of lengths and styles, but they almost all fall into one of three basic types of bridges: beam, arch, or suspension bridges.

The main difference between the three types of bridges is what distance they can cross in a single span. A span is how far it is between bridge supports, which can be columns, towers or even the walls of a canyon.

Beam bridges consist of a horizontal beam (often concrete or steel) supported at each end by columns or piers. The weight of the beam and traffic on the bridge is directly supported by the piers. The farther apart the piers are, the weaker the beam will be. This is why beam bridges usually span no more than 250 feet. They’re common on highway overpasses. Some beam bridges use supporting lattice work — called a truss — to add strength.

Arch bridges have great natural strength due to their shape. Semicircular in shape with abutments on each end, arch bridges are usually made of steel or concrete and can span up to 800 feet. The shape of arch bridges naturally distributes weight away from the center toward the abutments.

Suspension bridges use cables strung across tall towers to support the bridge surface, called the deck. Because the cables and the towers can distribute a tremendous amount of weight, suspension bridges can span from 2,000 to 7,000 feet! Almost all suspension bridges also have supporting truss systems underneath the bridge deck to add strength and support.

So how long are some of the longest bridges in the world? Because there are different ways to measure the length of bridges, a bridge can be the longest bridge in one of many categories. For example, China’s Danyang-Kunshan Grand Bridge holds an elevated high-speed rail line and spans over 102 miles. China also is home to the world’s longest sea bridge: the 26.4-mile Qingdoo Haiwan Bridge.


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    • Good morning, Kerrick Elementary 2nd/EBD! Thanks for another great comment today! We thought the time-lapse was awesome, too! We especially loved watching all the itty bitty boats going really, really fast! :-)

  1. We shared this as our first wonder of the school year today. They loved the video and one of my students even knew it was time lapsed so exciting. Introduced them to the different parts of the WONDER.
    Also had a great discussion about the different types of bridges just looking at the pictures -compare/contrast. Great thinking!!

    • Welcome to Wonderopolis, Mrs. Caplin’s Class!

      We’re so glad that you liked this Wonder of the Day® and chose it to “bridge” summertime and the new school year! We look forward to learning together with you and receiving lots of GREAT comments from you this year! :-)

  2. Today in language arts, I learned that China has one of the longest bridges in the world but I believe this WONDER!! I also believe it because I live in Australia and I traveled to California and biked on the Golden Gate Bridge!!! :)

    • WOW, Liam! What a WONDERful adventure you had traveling to America and visiting California! We think it must have been AWESOME to take a bike ride across the Golden Gate Bridge! Thanks for sharing your personal connection to this Wonder of the Day®! :-)

  3. Well I thought the bridge wasn’t that long, so now I know. Do you know what the biggest bridge in the world is? I do! Can you guess?

    • Please tell us! Did you find the answer in a book? Did you research “the world’s longest bridge” online? Thanks for WONDERing with us today, Wonderfriend! :)

  4. I learned how long the bridge is. I enjoyed this because it was fascinating about the facts that were given. I didn’t know that this was the longest bridge, I thought it was another bridge!

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Have you ever wondered…

  • How long is the longest bridge?
  • What are the three main types of bridges?
  • How many bridges are there in the United States?

Wonder Gallery

bridge_shutterstock_12331150Vimeo Video

Try It Out

Ready to cross the bridge to see what’s on the other side? Find a friend or family member to adventure with you as you explore one or more of the following activities:

  • Get a closer look at some of the longest bridges in the world. Jump online to explore these amazing bridges:
    • Danyang–Kunshan Grand Bridge: Located in China, the Danyang-Kunshan Grand Bridge does not span water. It is used for an elevated high-speed rail line and totals over 102 miles in length.
    • Qingdao Haiwan Bridge: Also in China, the Qingdao Haiwan Bridge opened in 2011 and is now the world’s longest sea bridge at 26.4 miles in length.
    • Lake Pontchartrain Causeway: The longest bridge in the United States consists of two parallel bridges across Lake Pontchartrain in southern Louisiana. The longer of the two bridges measures 23.87 miles long and is the seventh-longest in the world and the second-longest over water.
  • If you think you might one day want to be an engineer or a city planner, you’ll need to learn even more about bridges. For a fun, interactive activity, visit the PBS Building Big site to take The Bridge Challenge. If you want to review a bit before taking the challenge, stop by Bridge Basics first.
  • Are you up for a challenge? Modern engineers around the world face daily challenges to design bridges to create new pathways for travel. Some of the challenges they face can be seen with simple experiments at home. Grab a plain piece of notebook paper, six books, 100 pennies, and a ruler. Your challenge? Make a Paper Bridge that can support 100 pennies! Check out the link for directions and tips.


Still Wondering

To learn more about various engineering career paths, check out Science NetLinks’ Discover Engineering lesson!


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