Since about 4000 BCE, paved roads have allowed humans to travel, communicate, and trade more efficiently. Advancements in road construction contributed to the urbanization of settlements, as well as significantly improved military maneuvers and transport.
The first roads were more like dirt paths or game trails, over which humans carried packs, and eventually, horses or oxen pulled carts. Over time, these developed to allow transportation, communication, trade, and governance across large regions. It wasn’t long after the invention of the wheel that humans realized that it was difficult to transport heavier loads over dirt paths, and they started to construct roads. The oldest paved roads were made of stone and were in the Indian subcontinent and Mesopotamia, specifically the cities of Ur and Babylon.
The Romans experimented with techniques to build durable roads, particularly to help legions move throughout the empire more easily. Some of the roads they constructed are still used today. The Romans used several layers of materials on top of a deep foundation of crushed stone; a technique that still forms the basis of how roads are constructed today. It wasn't until the 18th century that a Scottish man named John Metcalfe started to further the techniques of road construction.
John Metcalfe built many roads and bridges in Yorkshire, England. The roads were built in three layers: the first consisted of large stones, the second a mixture of road materials, and the third a layer of gravel. Two Scottish engineers, Thomas Telford and John Loudon McAdam, are known for modernizing roads by created the system of raising the foundation in the center of the road to allow easy water drainage. McAdam enhanced road construction by topping roads with soil and crushed stone aggregate, which was packed down by rollers. His design was called "Macadam" and led to the creation of Tarmacadam, which is known as tar. One of the first uses of tar and asphalt was in Paris in 1824. One of the first paved roads in America was Pennsylvania Avenue in Washington, D.C.
Roads in America today are mostly paved with asphalt concrete. Asphalt concrete is mainly made by adding asphalt cement to sand and rock. However, special care is required to construct and pave roads on which traffic is heavy, so asphalt cement is often modified with other materials like polymers to increase stability and reduce the distress of the roads. There are many types of binders, and it is important to select the appropriate one for the specific climate. Other measures are taken to ensure roads can support the weight of the heavy trucks that fill the highways. Paved roads are now engineered to be more durable, enhance skid-resistance, improve safety, etc.
The actual construction of the roads has also changed a lot over the last century. Groups of workers, equipped with picks and shovels, used to build roads, but now workers operate heavy machinery. Roads are also rebuilt by tearing up the existing pavement, grinding it, and dumping it into trucks that will transport the materials to be reused as aggregate for new roads. After the road has been torn up, other machines grade the surface, pave it using fresh sheets of asphalt, and then a roller smooths the surface. Larger networks of roads and wider roads were built as the need for transport - especially for military purposes - and trade and communication increased. Nowadays, we couldn't get to work, to the hospital, to school, to the store, or do many of our daily activities without roads.
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