Thousands of years before urban planning, motor vehicles or even the wheel. Our first roads were spontaneously formed by humans and animals walking the same paths over and over to get water and find food. As small groups of people combined into villages, towns and cities; networks of walking paths eventually became what we now consider most roads. The first roads really appeared all over in places like the woods, open terrain, even following shore lines.
Following the introduction of the wheel approximately 7,000 years ago; larger and heavier loads could be transported longer distances. These loads showed the limitations of dirt paths, as they turned into muddy bogs when it rained. The earliest stone paved roads have been traced to about 4,000 B. C. in the Indian subcontinent and Mesopotamia. The Romans developed techniques to build roads using multiple layers of materials of crushed stone. They used crushed stone to help with the water drainage. This process allowed their legions to be more mobile throughout their empire. Some of those roads remain in use today more than 2,000 years later. These practices were the foundation of the techniques we use on building today’s roads all these years later.
The modern road construction techniques can be traced to a process developed by Scottish engineer John McAdam. In the early 19th century McAdam topped multi-layer roadbeds with a soil and crushed stone aggregate that was packed down with heavy rollers to compact it all together. Contemporary asphalt roads capable of supporting the vehicles that emerged in the 20th century built upon McAdam’s methods of compacted base of processed stone and then tar was added as a binder. The actual process of road building has changed dramatically over the past century, going from large groups of workers with picks and shovels to what we use today as enormous specialized machines.
With much of the 20th century punctuated by hot & cold wars, the need to move the military just as the Romans did led to the development of the modern superhighway, including the German Autobahn and our American interstate system. Military requirements for long unobstructed stretches that could be used as emergency runways for aircraft paid a dividend for civilian drivers who could now cross countries at high speeds much more efficiently than a dirt road. Making these travels much safer and efficient for everyone.
Building or expanding modern roads is a complex undertaking that can cost anywhere from $2 to $12 million per mile depending on the number of lanes and the location. A great deal of consideration is put into where roads should go in order to minimize disruptions and make them as direct as possible. While simultaneously keeping slopes reasonable in hilly areas for performance and safety reasons.
Today we use the practice of rebuilding existing roads. This process always starts with machines pulling up (milling or pulverizing) the existing pavement. The grindings that are pulled up are either used as part of the new base or are put into trucks for reuse later as aggregate for new roads. After grading and compacting the surface, pavers come in and lay down fresh continuous sheets of asphalt followed directly by the rollers. This process allows the asphalt and stone to bind together with the tar material for a smooth surface for pedestrian, bicycle and vehicular traffic.
Needless to say the engineering and process we use today has come a long way from the walking paths our ancestors and animals made through the lands centuries ago. Today we have an abundant amount of options to get from place to place because of those paths and the ability to create roadways. To think that just about 150 years ago there were no vehicles; everything used for long distance transportation was generally horse and buggy or trains. We have come a long way in a short amount of time in history.