Months or even years of planning go into road building. Before the type of road and its final route are determined, engineers typically analyze the expected traffic, the road’s location and underlying geology, local land ownership, environmental impacts, material characteristics and availability, and cost. Public meetings are held. Bids are solicited. And only after all these items have been ironed out, does construction begin. 

Whether roads are paved or unpaved, made of dirt, concrete, hardwood or other specialized materials depends on their use, location and available funding. For example, roads in undeveloped or very rural areas tend to be unpaved while those that handle high traffic volumes from one end of our nation to the other are paved concrete highways. 

While some of this may seem intuitive, do you know why some roads are have a concrete surface while others are paved with asphalt? Are you aware that unpaved roads may be simple dirt paths while others are improved with layers of crushed gravel? And what materials are used to construct specialty roads, such as construction access and earthquake-resistant roads?

The accompanying infographic offers a brief look into the construction materials for diverse types of roads. The next time you take a long drive, especially one that winds through both urban and rural areas, think about where you are, the reason for the road and the amount of  traffic you encounter — and you’ll gain a better understanding of the fascinating world of road construction.