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 (a bridge over a road instead of a body of water) 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!
(10 votes, avg. 4.90 out of 5) 
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Hello wonderopolis, do roads freeze because the metal gets cold and all that metal from the cars?
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!
Wonderopolis, can you make one that has a video not from youtube so that my school Woodcrest can watch it?
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.
I LOVE YOU WONDROPOLIS.
What a SUPER nice thing to say, Ashley! It makes us really happy to know that you enjoy learning in Wonderopolis!
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!
That is so cool Wonder of the day!
We’re SO GLAD you thought today’s Wonder was COOL, Julia! Thanks for letting us know that!
That is so neat!
We thought exploring today’s Wonder was really NEAT, too, Julia! Thanks for being a GREAT Wonder Friend!
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!
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!
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!
And Wonderopolis sorry for making the comment so late Wonderopolis.
BYE see you tomorrow
Mushkale from Mrs.T’s class
That’s OK, Mushkale! We’re just really thankful that you enjoy visiting Wonderopolis!
I think it is because it is metal, and this is a good wonder.
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 Wonderopolis. Do you have any wonders about hockey (ice hockey)?
Hi, Mushkale! Have you had a chance to visit these past Wonders (below) that have something to do with HOCKEY yet? We think you will really like them!
Wonder #109 – What Is a Zamboni®? http://wonderopolis.org/wonder/what-is-a-zamboni%C2%AE/
Wonder #67 – When Were Ice Skates Invented? http://wonderopolis.org/wonder/when-were-ice-skates-invented/
Happy WONDERing!
Wow.
Thanks for another great “wow” on a Wonder, today, Wow Girl! We appreciate your enthusiasm for Wonderopolis!
This was very cool to watch. I love you, wonderopolis. Thank you.
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!
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
We think it’s SUPER that you are going to remind your parents about bridges on a cold day, Team Unger 4! That ROCKS! We haven’t been to the Golden Gate Bridge, but we’ve WONDERed about it! You can, too, by exploring this great Wonder of the Day® about super long bridges:
Wonder #236 – How Long Is the Longest Bridge? http://wonderopolis.org/wonder/how-long-is-the-longest-bridge/.
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!