Bouncy bus ride? Welcome to pothole season.


You might suggest that Mom and Dad avoid driving over the potholes at the intersection of 14th Street and Madison Drive in Washington. They’re big ones! (Bill O'Leary/The Washington Post)
March 2

Have you noticed that the roads are really bumpy this winter? Maybe your school bus has gone BAM, causing the book you’re reading to smack you in the nose. Or maybe you have heard your dad curse after spilling his coffee because the car suddenly jerked up and down. If so, you have experienced one of the most dreaded adversaries in the civilized world: the pothole.

The reason the roads are particularly bad this year has to do with the freezing weather we have been having. But it takes more than cold air to create a pothole. The most important ingredient (other than the road) is water. What? How can the molecule that’s responsible for life be the source of the concrete devil?

What is water?

Water exists in three physical states: liquid, gas and solid. The water you see most often is in the liquid form. In addition to drinking and swimming in water, we also breathe its gas form. That’s right: Water vapor is a component of the air we breathe. To be specific, air is made up of the following substances:

●oxygen: 21 percent.

●nitrogen: 78 percent.

●water vapor, carbon dioxide and other gases: 1 percent.

Water also exists as a solid, otherwise known as ice, and that’s where the trouble starts. When water freezes, it expands (gets bigger). You can witness this phenomenon by placing a nearly full and capped plastic bottle of water in the freezer. When the water freezes, it will expand and distort the bottle. (If you fill it all the way, the bottle may crack.)

The birth of the pothole

Although roads are built to withstand lots of pressure, their surface develops cracks over time. That happens because cars and trucks are so heavy and because the pavement expands and contracts (gets smaller) in response to temperature changes. Potholes can occur in areas that don’t get ice and snow, but they are more common in areas that do.

Water that gets into a road crack during the winter often freezes. As the water freezes, it expands, making the crack a little bigger. If more water gets into the crack and freezes, the crack gets bigger still. Eventually, this allows water to seep deeper into the road. As the water continues its downward journey, it weakens the structure of the road.

The average car weighs more than 3,000 pounds. That’s a lot of weight for roads to put up with, and weakened concrete or asphalt will eventually break down, leaving a jagged hole where the road used to be. Most potholes are the size of a grapefruit. Some, like the one shown in the picture, measure several feet across.

The best way to deal with potholes is to avoid them. Not only will that keep books from colliding with your head, but your dad won’t get in trouble for saying something he shouldn’t.

—Howard J. Bennett

Bennett is a Washington pediatrician. His Web site, www.howardjbennett.com, includes past KidsPost articles and other cool stuff.

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