2.2. History of highway engineering

The first mode of transport was by foot. These human pathways would have been developed for specific purposes leading to campsites, food, streams for drinking water etc. The next major mode of transport was the use of animals for transporting both men and materials. Since these loaded animals required more horizontal and vertical clearances than the walking man, track ways emerged. The invention of wheel in Mesopotamian civilization led to the development of animal-drawn vehicles. Then it became necessary that the road surface should be capable of carrying greater loads. Thus roads with harder surfaces emerged. To provide adequate strength to carry the wheels, the new ways tended to follow the sunny drier side of a path. These have led to the development of foot-paths. After the invention of wheel, animal-drawn vehicles were developed and the need for hard surface road emerged. Traces of such hard roads were obtained from various ancient civilizations dated as old as 3500 BC. The earliest authentic record of road was found from Assyrian empire constructed about 1900 BC.

In ancient times, people first traveled by walking, creating paths that were practical for reaching essential locations like food or water. With the domestication of animals, people began to transport goods and themselves in larger quantities, which required wider paths. The significant innovation of the wheel in Mesopotamia allowed for more efficient transportation with animal-drawn vehicles. This necessitated stronger road surfaces to support the weight of these vehicles, leading to the first hardened roads. Evidence of such early roads goes back as far as 3500 BC, showcasing how infrastructure began to adapt to human needs.

Think of ancient roads like the hiking trails we use today. At first, they were just simple paths made by repeated footfall, similar to how animals have created trails in nature. As we needed to transport heavier backpacks or supplies, just as with ancient cars, we would need those trails to be wider and stronger. Imagine inventing a cart that can hold more goods; you would naturally need to pave that trail for it to hold up against the weight.

The earliest large scale road construction is attributed to Romans who constructed an extensive system of roads radiating in many directions from Rome. They were a remarkable achievement and provided travel times across Europe, Asia Minor, and North Africa. Romans recognized that the fundamentals of good road construction were to provide good drainage, good material, and good workmanship. Their roads were very durable, and some are still existing. Roman roads were always constructed on a firm-formed subgrade strengthened where necessary with wooden piles. The roads were bordered on both sides by longitudinal drains. The next step was the construction of the agger. This was a raised formation up to a 1 meter high and 15 m wide and was constructed with materials excavated during the side drain construction. This was then topped with a sand leveling course. The agger contributed greatly to moisture control in the pavement.

Romans were pioneers in road construction, building an extensive network of roads that facilitated trade and military movement throughout their empire. Their roads featured advanced drainage systems to prevent water damage and were built with quality materials to enhance durability. Each road was constructed on a well-prepared base, often using raised foundations called aggers to help manage moisture, ensuring stable pathways for travelers. This systemic approach not only made travel faster but also allowed for consistent maintenance and longevity of the road structures.

Consider the Roman roads as the highways of today. Just like modern highways need proper drainage systems to handle rainwater and prevent flooding, Roman engineers understood that building roads with effective water management would significantly extend their life. Imagine building a well-crafted road with automatic drainage systems; it remains passable and safe, much like how Romans kept their roads functional for centuries.

The next major development in road construction occurred during the regime of Napoleon. The significant contributions were given by Tresaguet in 1764 and a typical cross-section of this road is given in Figure 2:2. He developed a cheaper method of construction than the lavish and locally unsuccessful revival of Roman practice. The pavement used 200 mm pieces of quarried stone of a more compact form and shaped such that they had at least one flat side which was placed on a compact formation. Smaller pieces of broken stones were then compacted into the spaces between larger stones to provide a level surface. Finally, the running layer was made with a layer of 25 mm sized broken stones.

During Napoleon's era, significant advancements in road construction took place, notably with the work of engineer Tresaguet. He moved away from Roman methods, opting for a more economical solution that utilized smaller stone pieces compacted together, yielding a durable surface for traffic. This innovative layering not only provided an effective path but also emphasized the necessity of drainage to prevent issues common in less thought-out designs. This marked a shift towards considering cost-efficiency in road construction without compromising quality.

Imagine building a house: instead of using whole bricks that might be expensive or heavy, you might use smaller, compact bricks that fit together well, just like Tresaguet’s road construction method. The smaller pieces fill in the gaps, creating a stronger structure. You can also think about a puzzle where each piece needs to connect perfectly, allowing water to drain away, keeping the entire puzzle intact.

The British government also gave importance to road construction. The British engineer John Macadam introduced what can be considered as the first scientific road construction method. Stone size was an important element of Macadam's recipe. By empirical observation of many roads, he came to realize that 250 mm layers of well compacted broken angular stone would provide the same strength and stiffness and a better running surface than an expensive pavement founded on large stone blocks.

John Macadam revolutionized road construction methodology by emphasizing the importance of stone size and layering. His approach was systematic, using smaller, broken stones compacted tightly together to create a solid road surface. This scientific basis of road construction ensured cheaper requirements for materials while maintaining high standards of durability and ease of travel. Macadam's principles laid the groundwork for modern road construction practices.

Think of Macadam's method like making a cake with layers. Instead of making one massive cake, you build it with smaller, stacked layers of sponge that fit snugly on one another. Just like these layers make a cake more stable and enjoyable, Macadam's small stones created a strong, smooth surface for vehicles to travel on.

The modern roads by and large follow Macadam’s construction method. Use of bituminous concrete and cement concrete are the most important developments. Various advanced and cost-effective construction technologies are used. Development of new equipment helps in the faster construction of roads.

Today's roads generally adhere to the foundational principles established by John Macadam, particularly concerning layered construction using quality materials. The introduction of bituminous and cement concrete has enhanced road durability and safety. Additionally, modern technology with advanced construction machinery has expedited the building process, allowing for better road quality and efficiency.

Imagine upgrading from hand tools to power tools in construction. This is what happened with road building: by utilizing inventions like modern paving equipment, constructing roads is faster and results in a much stronger and durable surface. Just like how power tools turn hours of labor into moments of efficiency, modern road technologies optimize the building process.

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