There you sit in the backseat. Mile after mile passes by on the lonesome highway. Every once in a while, you notice a little green sign with a number on it. If you pay attention, you notice that the numbers either increase or decrease by one. What are these things? Highway mile markers, of course!

You can find mile markers along all sorts of highways. Some are local or state highways, while others may be large interstate highways. Have you ever seen these mile markers and WONDERed why they're there?

It's a good thing to WONDER about, after all. What purpose could a small green sign with the number “137" on it possibly have? As it turns out, mile markers serve several important purposes.

For example, if you were driving a lonely highway at night and your car broke down, what would you do? You would probably call someone for assistance, such as the police. But did you ever stop to think how you'd tell them where you are?

Telling them you're on Highway 37 near the big oak tree with the funny bend in it probably isn't going to help all that much. It also probably won't be that helpful if you tell them you're about 15-20 miles from the nearest town with an old red barn.

If you can tell them you're only about a quarter-mile past mile marker 23, though, you'll probably get the assistance you need fairly quickly. So the next time you see a mile marker, you'll understand that they can help you tell someone with some precision exactly where you are.

On most highways, the mile markers also coordinate with the exit numbers. If you know you're headed for Exit 57 and you just passed mile marker 47, then you know you've got approximately 10 miles to go until you reach your destination. In this way, mile markers can help you keep track of where you are and how far away you are from certain exits.

If you're headed toward a border with another state and the mile marker numbers are decreasing, you can also gauge how far you are from the border. Most highways change mile marker numbering at state borders.

Mile markers on interstate highways can also help you determine which direction you're going. On most interstates, mile marker numbers begin at the south state line on north-south routes and increase as you travel north. On east-west routes, the numbers begin on the western state border and increase as you travel east.