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Roads are built with various materials depending on their intended use and public demand. Dirt roads were common in the past, but engineers developed new ways to create long-term roads using sand, gravel, tar, paving bricks, asphalt, or concrete. Asphalt is cheap and easy to apply, while concrete lasts longer but needs reinforcement. Some older cities have brick or stone streets that were paved over with asphalt. Specialized roads may use rubber or recycled metals. Corduroy roads were made of split wood logs.
Different roads are built with different materials, depending on their intended uses and public demand. Conventional ones intended for long-term automobile traffic are often built in layers, which may include sand, gravel, tar, paving bricks, asphalt, or concrete. Roads specialized for commercial uses may use other materials such as rubber or recycled metals. Some of the earliest ones in the United States were actually built of split wood logs arranged in tight rows. These were called Corduroy Roads.
Perhaps the most common material used for roads is dirt. As humans and primitive machines walked the line of least resistance across the landscape, furrows would have formed in the ground itself. As property rights established for landowners, these early dirt roads often formed along property lines. There was little formal creation during these early days, but individuals were free to make improvements such as weed removal and bridge construction.
As the need for better roads grew, engineers developed new ways to create them for long-term use. Sand, gravel and various tars were used to establish official roads for pedestrians and wheeled transport. While they were an improvement over the ungraded and often impassable dirt trails, they were still at the mercy of Mother Nature and the weather.
In the 1920s many new roads were built using a relatively new mix of waste material derived from crude oil and gravel called asphalt concrete. Asphalt could be poured onto a prepared bed of sand and gravel to form a firm but malleable surface. Cars could drive over the asphalt surface without causing much damage, although the constant stresses caused by traffic can cause the asphalt to warp over time. Asphalt is still used to build roads, mainly because it is cheap to produce and easy to apply.
For greater durability, some roads are built of concrete. Concrete usually lasts longer than asphalt, but it also tends to crack and splinter if not reinforced with rebar or divided into smaller sections, much like a sidewalk. Sections of concrete are often pieced together to form roads, although some may be built on site through the use of wooden forms.
Some streets in older cities may have been built with brick pavers or smooth stones. Masons or stonemasons would place the pavers on a prepared bed and use mortar or cement to hold the individual stones in place. As the use of asphalt became more popular, many of these brick and stone streets were simply paved. Occasionally the asphalt layer will be worn away, revealing the bricks or other materials originally used.
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