Roads and Highways

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Roads and highways have been principal means by which entire economies and societies have emerged and grown over time. They have contributed positively to the spread of ideas, cultures, languages, inventions, goods, and services. Disease, enslavement, tribute, and warfare have also spread through networks of roads and highways to devastate entire peoples and areas and immeasurably alter the course of history.

Early Roads and Highways

The first roads dating back to the dawn of civilizations
(c. 3000 b.c.e.) were little more than dirt paths worn down by frequent travel from one location to another via wheeled vehicles. Rivers were the main highways of this time period, as goods and people moved up and down their courses and any city that desired to rise to importance was located on a river. Yet within a period of a few hundreds of years, roads became a commonplace and began to reshape the geopolitical history of entire regions. Even during this period, rivers continued to be the most economical way to transport large quantities of goods, with roads being used to link river trade to cities and towns throughout entire regions.

The earliest roads were designed to bear the weight of wheeled traffic including carts, large wagons, and swift chariots. Within cities the main thoroughfares were paved and varied in width from two to ten meters. A series of "narrow streets" connected to these "broad streets" within cities and enabled populations within them to increase substantially in size. The Neo-Babylonians and Assyrians constructed royal roads that linked major cities across their empires. The Persians took over many of the practices of the Assyrians and maintained excellent royal roads, some as long as 2,670 kilometers (1,650 miles). These roads featured "excellent inns," as noted by the Greek historian Herodotus (c. 485–c. 425 b.c.e.), as well as special parks so that the king or his senior administrators could take their rest in leisure when traveling across the vast reaches of the Persian Empire. Similarly, in ancient Egypt roads were constructed both within large cities and linking cities and regions of Egypt and her territories to one another. The typical Egyptian road was about five meters in width. Outside of cities, most roads in the ancient Near East were unpaved but had been carefully prepared and leveled, and were regularly maintained. The ancient Greeks did not favor roads and built only a skeleton of dirt roads from one region to another until the time of Alexander the Great (356–323 b.c.e.), who saw the need for better roads linking the rapidly expanding segments of his empire.

The Romans, likely expanding upon earlier techniques of the Etruscans, took road building to new heights of engineering excellence, constructing two, four, six, and eight lane highways connecting all key parts of the Empire. Roads themselves became a symbol of the might of Rome and the certainty that if they were needed, a Roman army would arrive swiftly to deal with any sociopolitical unrest or the incursion of enemies from outside its borders. Roman surveyors determined the optimum location and direction of roads, favoring straight traces whenever possible. Roman engineers constructed roads that would last for centuries through careful attention to the underlying base materials, superb drainage to keep water away from the road and its foundation, the careful use of stones and cement, and regular repair. Many miles of these Roman roads survive throughout the former Empire and quite a few modern roads follow the exact course as their Roman predecessors. While originally designed for military purposes, the roads became the means by which Roman ideas, life, and culture spread across the Empire. All roads carried mileage markers, always delineated in terms of their distance from the imperial city of Rome, a reminder to all of the might and power of the Empire. By the time of Diocletian (245–c. 313), there were 372 main roads throughout the Empire, covering a distance of some 85,000 km (nearly 53,000 miles). The Romans went well beyond any of their predecessors in the extent and interconnectivity of the system of secondary and primary roads they created and maintained across the Empire. In Roman Britain alone, more than 9,656 km (6,000 miles) of roads were constructed and maintained. Bridges and tunnels, milestones to enable travelers to instantly know their location, wooden signposts, and many other "modern" features of roads and highways were common throughout the Empire. The roads created ideal conditions for the growth of a postal service for government use and also a private postal service employed by wealthy citizens. A series of posts were set up so that couriers only had to move from one posting station to another—a design that would later be used by the famous but short-lived Pony Express in the American West.

Roads were not a distinctly Roman and European phenomena. The Qin and Han dynasties of China created a highly integrated network of roads, mainly for military use, in the second century b.c.e. The first Qin Emperor, Qin Shihuangdi (c. 259–210 b.c.e.) constructed 7,000 km (4,350 miles) of roads radiating out from his capital city of Xianyang in northern China. One hundred years later, there were more than 35,000 km (21,750 miles) of roads in northern China serving an empire of some 4 million square kilometers (1.5 million square miles). Similarly, the Incas created an empire running from Ecuador to central Chile and held it together via a network of more than 10,000 roads built across some of the most difficult mountain terrain in the world. Remnants of these Incan royal highways still exist in the early twenty-first century, and many modern roads follow the traces of these roads as a continuing tribute to the foresight and skills of these early highway engineers in South America.

The road systems developed by the Romans throughout the western Empire declined considerably after the fall of Rome, while those in the East continued to be maintained to a reasonable degree both under the Eastern Roman emperors and their Muslim conquerors. Many medieval roads in Europe declined to little more than dirt roads and were subject to flash floods and steady deterioration.

Modern Roads and Highways

Roads in the West began to be vigorously revived in the seventeenth century with the introduction of street lighting, ferry services, and emerging regulations from local, regional, and national governments. Central governments began to assume more direct responsibility and control for roads and centralized planning and maintenance became common, supported by general tax revenues.

Pierre Trésaguet (1716–1796), director of the École des Ponts et Chaussées in Paris in the mid-eighteenth century, had studied long and well the achievements of the Romans. His department had responsibility for some 40,000 km (25,000 miles) of roads throughout France, many built in the exact traces of earlier Roman roads. Trésaguet ensured that exacting road preparation methods were employed, following earlier Roman techniques, and the road system throughout France improved dramatically under his tenure. Two Scottish engineers made similar improvements throughout Britain in the early nineteenth century. Thomas Telford (1757–1834) built an exquisite model road between London and Holyhead demonstrating the superiority of preparing a very solid and carefully constructed roadbed before providing surfacing materials. While expensive to build, it was vastly superior to other roads. John McAdam (1756–1836), his fellow Scot, pioneered the use of natural materials as the base of a roadbed and developed methods to highly compact these materials to provide the same type of firmness that Telford achieved, only with much lower production costs. The surface material used on his road and the entire type of road took its name after him—macadam. By the late nineteenth century, the use of asphalt and portland cement (first used in Scotland in 1865) also became common and the maintenance required for roads became much less labor intensive.

Roads, including early toll roads such as the Lancaster Turnpike in Pennsylvania where travelers had to pay a fee to enter and/or exit the road, were a principal means of commerce in colonial America, and traces to the American West eventually were turned into roads that enabled white settlers to push rapidly westward in search of new lands and opportunities.

The advent of trains and railroads in North America, Europe, and elsewhere provided new opportunities to create many smaller secondary roads that linked many smaller towns and farming areas to commercial nodes. Consequently, these roads became the means by which goods and services circulated far more widely than was economically feasible before with attendant mobility of goods, people, and ideas. The combination of railroads and roads during the Civil War, for example, enabled large and rapid movements of troops and influenced the outcome of many a Civil War battle.

The nineteenth century saw the introduction of steam-powered equipment to construct roads, with the most important invention being the steamroller of Louis Lemoine and Amedee Jean Ballaison. These steamrollers quickly found their way to India and other nations far from Europe and the United States. New gasoline powered vehicles provided even more powerful machines to build roads and also led to more plentiful traffic for roads, resulting in yet further expansion of networks of roads across nations. By the nineteenth century it was common for city roads to be made of portland cement, and bitumen (pitch) or concrete used for cross country routes. Rural roads in the hinterlands continued to consist of dirt and packed gravel.

The first multi-lane, limited access highway in North America was constructed during 1917–1925 as the Bronx River Parkway, a New York thoroughfare still in use in the twenty-first century. The first bona fide superhighway in the United States was the 160-mile Pennsylvania Turnpike from Middlesex to Pittsburgh that opened in 1940 and quickly outdistanced expectations as 2.4 million vehicles used it annually within the first few years. Adolf Hitler (1889–1945) and Benito Mussolini (1883–1945) were aficionados of superhighways, and under their direction, massive superhighways were constructed in Italy and Germany in the 1930s that enabled the rapid movement of troops. President Franklin Delano Roosevelt appointed a National Inter-regional Highway Commission in 1941 and a Federal Aid Highway Act was approved in 1944 that authorized $1.5 billion for interstate highway construction. By the time of the Eisenhower administration, the federal highway legislation resulted in the construction of more than 64,000 km (40,000 miles) of highways running across the United States in both north and south and east and west orientations. Many states, such as New York, Pennsylvania, Ohio, and Illinois, also built their own extensive toll roads that connected in networks running particularly throughout the northeast. In the early twenty-first century similar highway systems can be found throughout the world, and the proportional number of miles of such highways within a nation serves as a rough gauge of its economic status in the world. These massive networks of superhighways and their linked secondary roads enabled the massive growth of suburbs and attendant suburban "flight," substantially altering the tax base and quality of life of central cities–a situation readily observed in places such as Atlanta, Boston, Chicago, London, Los Angeles, Paris, and Philadelphia.

Highway Engineering and Ethical Issues

Highway planning in the early 2000s is a complex branch of civil engineering that is designed to move goods and people efficiently, effectively, and safely across large distances. It includes attention to forecasting demand, acquiring land from various parties, designing roads and arteries that make for safe and aesthetically pleasing experiences for highway users, moderating costs, and providing for long-term maintenance and expansion when needed. Traffic volume is generally measured in terms of annual average daily traffic, which allows for derivation of a figure that avoids the inevitable peaks and troughs of traffic flow in any given day, week, or month. An entire route is divided into zones and then estimates are made about travel between zones and the amount of travel that will be undertaken by different modes of transport (for example, trucks, cars, buses). A maximum theoretical traffic flow rate is calculated using reasonable parameters of environmental, highway, and traffic conditions. A further factor taken into account in planning is what level of service the road will need to bear that will be acceptable to its users. Travel is an inherently subjective experience, and planners attempt to find an acceptable level of service (LOS), avoiding the extremes of very good (index A) and very poor (index F).

A number of additional factors need to be considered. All human technological applications have environmental effects. Highways directly affect matters such as noise pollution from horns, tires on road surfaces, engines, the speed of traffic, and shock effects from heavy loads on road surfaces; air pollution due to carbon monoxide, nitrogen oxides, volatile hydrocarbons, sulfur oxides, and particulate matter from exhaust fumes as well as evaporation from road surfaces; water pollution due to runoff that picks up oils, trash, and other materials from road surfaces; and environmental effects from the initial siting of the highway and its continued maintenance. These latter effects can include changing migration patterns and habitats of birds, mammals, amphibians, fish, and other creatures, as well as increased road kills (which number substantially more than one million mammals per year in America alone). Sometimes road kills result in the total extinction of a species or a severe threatening of its existence, such as with the Florida panthers.

Highway design includes attention to both aesthetics and safety issues. Each highway has to surmount certain physical challenges that the land presents, and decisions have to be made about how much to use the natural features of the land in construction or to substantially alter them. Modern highways attempt to utilize natural materials and natural roadbeds as much as possible, because it is far cheaper than completely excavating and hauling away such materials and replacing them with others. Sometimes the natural material base is not conducive to the type of heavy travel a particular road will be required to bear and then such steps have to taken.

A much larger portion of land is required than just that needed for the roadway itself. Most highways require a median that is almost equal in size to the width of the one or more lanes on one side of a divided highway. Then the outer edge of the driving lane requires a shoulder so that vehicles have a space to move off the road safely when they encounter vehicular or other problems. A drainage ditch is usually found outside the shoulder to handle runoff from the driving lanes, which are sloped in such a way that water runs off the highway quickly. The ditch also serves as the means to handle runoff from surrounding land on either side of the road cut to keep water off the road surface and prevent erosion from undermining the pavement or roadbed.

Pavement materials for roads and highways have to meet technical standards in order to be used. All materials must be sufficiently strong and durable to meet the required criteria that planners have established for that particular type of road. A typical highway is a composite of many different types of materials that are laid down in a carefully defined sequence and constantly checked to verify that they meet required specifications. Materials include sand, gravel, crushed rock, portland cement, asphaltic cement, lime, and, increasingly frequently, recycled materials such as crushed glass, scraps from old roadways, and pulverized tires.

Road geometry takes account of the steepness of curves, the slope of hills and valleys (road grades), passing maneuvers on varied terrain, and the need to maximize clear lines of sight. This is further complicated by situations where two highways meet one another, where a whole series of considerations must be addressed to plan and construct effective intersections and interchanges that enable a smooth and safe flow of traffic.

The actual siting of highways is always a complex decision that involves balancing factors such as travel time, vehicle operation cost, accessibility, environmental effects, societal acceptability, safety, total cost of construction, and viable alternative routes. Increasingly, local, state, and federal governments in many countries have to use the concept of eminent domain to assert their primary claim over land held by owners reluctant to relinquish their claims, frequently because they are opposed to the siting of the highway through their property. Government agencies generally are required by law to provide a fair-market value price to the owners.

The impact of interstate highways on commerce, migration, immigration, and employment growth has been the subject of much study. The overall findings indicate that, in general, counties or administrative units that reside alongside interstate highways see an increase in net immigration, employment growth, and commercial activity, while counties that have been bypassed by the interstate suffer net migration, a loss of employment over time, and declining commercial activity. The large amounts of particulate matter generated from major roadways has been identified as a source of chronic exposure that produces negative health effects within communities, especially in children and adults suffering from various respiratory preconditions.

Roads and highways also have to be managed by agencies to ensure that traffic flow is maintained at a reasonable level and that users of the roadway obey traffic laws that are designed to maintain such flows. Traffic signals of many different varieties have been developed, and a set of international standards have been developed for signs so that drivers can travel virtually around the globe and know what they are supposed to do in particular situations. Toll booths, highway exit and entry, emergency breakdown services, quick response to traffic accidents, enforcing traffic laws, and many other facets of roads and highways are generally under-appreciated by users but essential to maintaining a working system of roads and highways. Driver error, including falling asleep at the wheel, is by far the most common source of traffic accidents and deaths and injuries to drivers, pedestrians, and wildlife.

Future Developments

Computerization is the next major innovation in roads and highways, and virtually every industrialized nation has a wide range of current applications in the area of intelligent transportation systems (ITS). These include automated toll booths where vehicles with appropriate stickers on their vehicles can pass through the booth and automatically be billed for their trip rather than having to stop and manually deliver money or tokens to a human or automated operator. Many interstates or roads in heavily congested areas of the world use computers to regulate entry into the highway as traffic lights and barriers allow only one vehicle at a time onto the highway such that mergers happen more seamlessly and the flow of traffic on the road is not impeded by entering traffic. Many cities have sophisticated computer systems that regulate traffic signals across the city with the timing of signals changing throughout the day to accommodate the daily ebb and flow of traffic to and from major zones within the city. Cameras placed in strategic positions in cities and mobile camera units elsewhere increasingly document speeding vehicles with attendant tickets being subsequently issued to the offenders. Global positioning technology makes it feasible to track vehicles anywhere in the world, and many large transport companies already utilize this technology to keep track of their vehicles both on the road and also across railroad systems in seamless global transportation networks that enable managers to ensure that their products arrive at required destinations in a timely manner and in good condition.

ITS planners have created plans for intermodal transport systems that utilize advanced telecommunications and computer systems to move goods across entire continents through underground tunnels or highways dedicated solely to the movement of freight. These intelligent systems would only require human operators on points of entry or exit within the system, and once on the network, goods could be accelerated greatly in their passage to desired destinations. Similar designs exist for automobiles of the future that would go on "autopilot" once the human operator had placed the vehicle on the superhighway. Computers would then guide the vehicle to the required exit point and then the human operator would take over control functions to move the vehicle safely off the superhighway. Such a system would alleviate the traffic jams so familiar to major interstate highway systems during peak flow times and enable resources to be used more efficiently.

The widespread use of ITS raises a host of ethical issues, many not particularly unique to these applications but part of a broad set of issues common to technological innovations. Increasingly the operators of these systems would have knowledge of one's whereabouts and be able to track the movement of a single individual across a city, state, or even potentially around the globe as these various systems come online and interconnect both operationally and informationally. Technical managers would also be able to shape human perceptions and experiences of reality by varying conditions on these systems—for example, deciding that today's optimal travel time from point A to point B will be 25.8 minutes, and programming the system to deliver these results. It should be noted, however, that highway engineers have always shaped human perceptions of the surrounding environment and influenced ways of life going back to where the first roads were constructed (all artifacts have politics, as Langdon Winner has argued), how structures actually are designed (for example, low bridges on the Wantagh Parkway in New York designed by Robert Moses (1888–1981) specifically to keep buses off the parkway), and via the distinct sociotechnical roles that engineers play in public policy making.


SEE ALSO Networks.


Adkins, Lesley, and Roy A. Adkins. (1994). Handbook to Life in Ancient Rome. New York: Facts on File. A one volume reliable reference that includes numerous references to Roman roads.

Astour, Michael C. (1995). "Overland Trade Routes in Ancient Western Asia." In Civilizations of the Ancient Near East, ed. Jack M. Sasson. New York: Scribners. A definitive treatise summarizing current historical and archaeological information on this topic.

Carlson, Daniel. (1995). At Road's End: Transportation and Land Use Choices for Communities. Washington, DC: Island Press. A study of the complex set of factors that should be considered in planning and siting of highways.

Chen, Wai-Fah, and J. Y. Richard Liew, eds. (2003). The Civil Engineering Handbook, 2nd edition. Boca Raton, FL: CRC Press. A massive standard reference work that provides copious details about the construction of highways and other matters in civil engineering.

Dorsey, David A. (1997). "Roads." In Volume 4 of The Oxford Encyclopedia of Archaeology in the Near East, ed. Eric M. Meyers. New York: Oxford University Press. A summary article by a noted expert on roads in the ancient world and particularly the Middle East.

Garrison, William L., and Jerry D. Ward. (2000). Tomorrow's Transportation: Changing Cities, Economies, and Lives. Boston, MA: Artech House. Explores key options and tradeoffs concerning future transportation needs, challenges, and opportunities.

Lewis, Tom. (1997). Divided Highways: Building the Interstate Highways, Transforming American Life. New York: Viking. A journalistic depiction of the ways in which interstate highways transform culture with a focus on the situation in the United States.

Motavalli, Jim. (2001). Breaking Gridlock: Moving Toward Transportation that Works. San Francisco: Sierra Club Books. Argues for a more environment-friendly approach to transportation systems while avoiding simplistic solutions.

Rose, Mark H., and Bruce E. Seely. (1990). "Getting the Interstate System Built: Road Engineers and the Implementation of Public Policy, 1955–1985." Journal of Policy History 2(1): 23–55. An important study of a neglected topic: How do engineers interact with policymakers to help shape public decisions about transportation systems?

Sachs, Wolfgang. (1992). For Love of the Automobile: Looking Back into the History of Our Desires, trans. Don Reneau. Berkeley: University of California Press. A provocative, wide-ranging, sociological study of the ways in which the automobile shapes desires and the ways in which automobiles are designed to appeal to basic human desires.

Sussman, Joseph. (2000). Introduction to Transportation Systems. Boston: Artech House. An expert summary of all major issues related to transportation systems that grew out of a course the author has taught on this topic for many years at the Massachusetts Institute of Technology.

Vance, James E., Jr. (1990). Capturing the Horizon: The Historical Geography of Transportation since the Sixteenth Century. Baltimore, MD: Johns Hopkins University Press. The definitive one-volume history in English of transportation in modern times.

Winner, Langdon (1986). The Whale and the Reactor: A Search for Limits in an Age of High Technology. Chicago: University Of Chicago Press. A series of important essays by a noted political scientist about technology; see especially chapter two, "Do Artifacts Have Politics?" for a discussion of Robert Moses and the Wantagh Parkway.