Generally speaking, the evolution of a road goes from dirt to gravel to asphalt. But some places have started moving in the other direction.

According to the National Cooperative Highway Research Program, local jurisdictions in 27 states -- including Nashville, Ind., above -- have opted to unpave some of their roads.

This can be a real money saver when the cost of repaving a two-lane road can be as high as $1 million per mile. The cost to convert back to a dirt road can range from $1,000 to $100,000 per mile.

Many of these newly unpaved roads have very low levels of traffic. But going to gravel is not without its own costs. Critics point to increased wear and tear on automobiles and rising levels of dust.