Reflective "heat" on the roads

I was curious if anyone here knew the cause of the reflective “heat” puddles that appear on road ways from a distance. Growing up in Texas, I saw these on the highways anytime the temperature broke 90 degrees (pretty darn often), and I’ve always wondered what the scientific reasoning is behind them. Thanks in advance for your help.

The (more or less) technical term for this is a mirage. They can occur anywhere that hot and cooler air overlap, have have been recognized for centuries, especially in deserts.

http://dictionary.reference.com/search?q=mirage

Yup, it’s a mirage, specifically an inferior mirage. Wikepedia has a nice little article on mirages, including the “heat puddles” you asked about. Here’s a stunning mirage over a lake, and the “Green Flash” mirage of the setting sun.

The phenomenon of “heat shimmer” or mirage is caused by refraction of light. Any time light crosses a boundary between materials of differing density, it is bent, or refracted. The degree of refraction is dependent on the magnitude of the change in density. Air just above the surface of the road (or sand) is superheated and thus less dense. The density change is slight, so the refraction is similarly small. Thus the mirage can only be seen at low angles (less than 5° or so), so are only visible from a distance. When you get closer, they disappear.

What you see in a mirage is a highly distorted view of the opposite horizon or whatever the light bounced off of before being refracted into your eyes.