Do you like to ride in the car with your parents? Many kids enjoy traveling with their parents. It’s fun to see new places you’ve never been before.

As you travel, do you play games in the car? One game many kids enjoy is finding certain types of road signs. If you live in an area with lots of bridges or overpasses, you may have seen signs that indicate that bridges freeze before roads. Have you ever wondered why?

At first, it may not seem to make sense. Why would bridges freeze before roads? A bridge or an overpass is just like a road, right? The air temperature feels the same if you’re standing on the road or the bridge.

Bridges do indeed freeze before roads, and there’s a good reason why. It all has to do with science!

As the air temperature decreases, the surface of both roads and bridges will begin to cool down. Bridges will cool more quickly — and ice will form faster on bridges — for a couple of reasons.

First, cold air surrounds the surface of a bridge from above and below. This means that bridges lose heat from both sides. Bridges have no way to trap heat, so they will ice rapidly as soon as the temperature decreases to the freezing point.

Roads, on the other hand, only lose heat from their surface. The ground below roads helps to trap in heat and keep roads from getting icy unless the temperature drops several degrees below freezing.

Another reason bridges freeze before roads is because they’re usually made of steel and concrete. Both steel and concrete conduct heat very well. Any heat a bridge manages to trap will be transferred to its surface quickly, where it will be lost to the air around it.

Roads are made of asphalt, which does not conduct heat very well. The heat trapped within and below a road will tend to stay there longer, lengthening the time it takes a road to freeze.

If you’re riding with your parents during the winter, help them keep an eye on the temperature. If it dips below freezing, remind them that bridges and overpasses will freeze quickly. If it has been raining or snowing recently, bridges and overpasses may ice over in a hurry. If necessary, slow down and use a little extra caution to prevent an accident!

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    • Thanks so much for stopping by today’s Wonder of the Day®, Ashley! Bridges and overpasses have no way to trap heat like the asphalt in the roads themselves. This causes them to freeze more quickly than the roads when temperatures drop low enough. We encourage you to re-explore today’s Wonder to learn more! :-)

    • We’re super sorry you and your classmates at Woodcrest are having trouble viewing some the videos that accompany the Wonders of the Day, Ashley! Some schools and school districts put internal “blocks” on websites and videos because they are in charge of making sure the content that students see while exploring the internet at school is safe for viewing. Because the videos we choose to accompany each Wonder are “borrowed” from many different places around the internet, like YouTube and Vimeo, it might be a “block” from your school or district that is keeping your class from seeing some of the Wonder videos. You might want to check with your teacher to see if he or she can ask about getting the block removed. :-)

    • What a SUPER nice thing to say, Ashley! It makes us really happy to know that you enjoy learning in Wonderopolis! :-)

  1. Hi wonderopolis!!! That video was great! I think that the ice comes before the bridge because if you go too fast on the bridge your car could slip go off the road or your car could go off the road and you’ll crash. I wonder why ice has to come before the bridge? Do you know wonderopolis? I predict… that tomorrow will be about scientist or coloring. Another reason bridges freeze before roads is because they’re usually made of steel and concrete. Both steel and concrete conduct heat very well. Any heat a bridge manages to trap will be transferred to its surface quickly, where it will it be lost to the air around it. If your riding with your parents in the winter, help them keep an eye on the temperature. If it dips below freezing, remind them that bridges and overpasses may ice over
    in a hurry. If necessary, slow down and use a little extra caution to prevent an accident!
    !Thanks!

    • Thanks for sharing all the GREAT things you learned about bridges icing over before roads, Andrew! We appreciate your comment and hope you had a WONDERful time exploring Wonderopolis today! :-)

  2. I thought last night about what tomorrow’s wonder is gonna be? It appears it’s about bridges! I look daily at wonderopolis with my class. I’m in Mr. Draper’s class.

    • Hi there, Clay! We think it ROCKS that you and the other AWESOME students in Mr. Draper’s class check out Wonderopolis each day! :-)

  3. I think that bridges are cool because they are like a road over something like a river! I love wonderopolis.org because there are things cool on here!

    • We think it’s SUPER fun to learn in Wonderopolis, and we’re glad to know that you do, too, Cassidy! We hope you had a WONDERful day today! :-)

  4. Hey Wonderopolis, I think that bridges are cool because they are like a road over something like a frozen river!! Anyways, I think that tomorrow’s wonder will be about April Fool’s Day.

    By: Mushkale from Mrs.T’s class

    • Thanks for sharing what you think about bridges and also for taking a guess about the next Wonder of the Day®, Mushkale! We think you ROCK! :-)

  5. And Wonderopolis sorry for making the comment so late Wonderopolis.
    BYE see you tomorrow

    Mushkale from Mrs.T’s class

    • Hi there, Tyler! Thanks for sharing your thoughts about why bridges freeze before roads! We appreciate you letting us know you thought this Wonder was good! :-)

    • Thanks for another great “wow” on a Wonder, today, Wow Girl! We appreciate your enthusiasm for Wonderopolis! :-)

    • It makes us super happy to know that you like learning in Wonderopolis and that you thought the video for this Wonder was cool to watch, Wonder Friend! You ROCK! :-)

  6. Wonderopolis,
    I loved the video you put for this topic. I learned two new words from this topic overpass is a bridge and asphalt is the small rocks on roads. I also learned that bridges freeze faster than roads because they can’t hold heat in. I will remind my parents to ride slowly on a cold day. Have you ever been to the Golden Gate Bridge?

    Thanks for making me wonder,
    Team Unger 4

  7. Thank you for this article! I wonder if Oregon asphalt paving companies have to worry about this with all of those bridges in Portland!

    • That’s a great Wonder, dkrycek! We are excited that you are WONDERing with us about frozen roads! Thanks for sharing your comment with us! :)

    • Thanks for your question, Rayvon! Even when we are very careful, our cars can still slip on the ice. Stay warm, and Keep WONDERing with us! :-)

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Have you ever wondered…

  • Why do bridges freeze before roads?
  • How does the ground beneath a road help it to retain heat?
  • Do bridges or roads conduct heat better?

Wonder Gallery

bridge_shutterstock_91619099dreamstime_xl_35270617 customdreamstime_xl_12817463 customdreamstime_xl_12785105 customVimeo Video

Try It Out

Brrrr! Today’s Wonder of the Day makes us want to reach for a blanket. Cozy up with a friend or family member and check out the following activities to learn more about the science behind freezing roads and bridges:

  • Even if you’re really careful, it’s still possible to get stranded on the road in icy and snowy conditions. Is your family vehicle prepared in case of such an emergency? Head out to the garage or driveway with an adult to check out the trunk of the family automobile. Do you have the things you might need to make the best of a bad situation? Read how to Put Together a Winter Car Emergency Kit online to learn more about the types of things you should have on-hand in case of a winter emergency!
  • Even though you may not be driving yet, it doesn’t hurt to learn a few safe driving tips for winter weather. Not only can you remind the adults you ride with about what to do in case of bad weather, you can also learn a lot about science and how vehicles operate differently in inclement weather.
  • Up for a challenge? Why not try some COOL science experiments? Click on the links below to learn about several different types of fun science experiments you can do at home. Each experiment below helps you learn more about the different states of water and how it switches between liquid, solid and gas.

Still Wondering

Use Science NetLinks’ Putting It All Together lesson to help children create, design and evaluate different structures, such as bridges and buildings.

 

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