Thousands of years before urban planning, motor vehicles, or even the wheel, the first roads appeared on the landscape. Just as molecules coalesced into cells and cells into more complex organisms, our first roads were spontaneously formed by humans 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 became more formal roads. Following the introduction of the wheel about 7,000 years ago, the larger, heavier loads that could be transported showed the limitations of dirt paths that 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.
To help support the movement of legions throughout their empire, the Romans developed techniques to build durable roads using multiple layers of materials atop of deep beds of crushed stone for water drainage. Some of those roads remain in use more than 2,000 years later, and the fundamental techniques form the basis of today's roads.
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 then packed down with heavy rollers to lock it all together. Contemporary asphalt roads capable of supporting the vehicles that emerged in the 20th century built upon McAdams' methods by adding tar as a binder.
The actual process of road building has changed dramatically over the past century, going from large gangs of workers with picks and shovels to enormous specialized machines. Rebuilding existing roads starts with peeling up existing pavement, grinding it and dumping it straight into trucks for reuse later as aggregate for new roads. After grading the surface, pavers come in and lay down fresh, continuous sheets of asphalt followed directly by the rollers.
With much of the 20th century punctuated by hot and 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 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 in relative safety.
Building or expanding modern roads is a complex undertaking that can cost anywhere from $2 to12 million per mile depending on the number of lanes and the location. A great deal of consideration must be put into where roads should go in order to minimize disruptions and the make them as direct as possible, while simultaneously keeping slopes reasonable in hilly areas for performance and safety reasons.
Given the economic and political complexities of building new roads, autonomous vehicles being developed by everyone from Audi and General Motors to Google may turn out to be the best long-term solution to addressing congestion and safety. These self-driving vehicles use arrays of sensors to monitor their surroundings, and wireless communications to talk to each other and the cloud. At some point in the foreseeable future, instead of adding more lanes to highways, we may actually be able to reduce them as we shift to vehicles that can see and hear far more than human drivers, enabling them to drive closer together while still avoiding collisions, thus requiring less roadway. We live in interesting times, indeed.