Road is a strip of land that provides routes for travel by automobiles and other wheeled vehicles. Roads within towns and cities are often called streets.
Roads and highways are vital lifelines. Farmers use them to ship their products to market. Trucks can transport manufactured products from one area to another. Roads carry automobiles, buses, bicycles, and other vehicles on business and pleasure trips.
Kinds of roads and highways
Local and secondary roads.
Local roads carry traffic within a local area. Secondary roads link small communities and connect local roads to main highways leading to more distant places.
Primary highways.
The most important roads generally are those that carry the greatest number of automobiles, trucks, and buses. These main roads, called primary highways, connect the larger communities.
Major types of primary highways include divided highways and controlled access highways. Divided highways are roads with four or more traffic lanes divided in the center with a strip of land, called a median strip. This strip separates vehicles going in opposite directions and helps prevent collisions.
Controlled access highways are designed to achieve safety and smooth traffic flow through the principle of controlled access. On fully controlled access highways, a vehicle can enter or leave a main highway only at certain locations called interchanges. Most of these interchanges are at main crossroads. Grade separations are often used to separate crossing streams of traffic. In a grade separation, one of the intersecting highways crosses over the other on a bridge. The two are connected by sloping, curved roadways called ramps.
With controlled access, no driveways from homes or commercial establishments connect directly with the main highway. Minor roads and streets pass over or under the road without connecting to it. Minor roads may also dead-end at the highway or connect with a service road that runs parallel to the highway.
Freeways or superhighways, called motorways in some countries, are main highways with full access control and grade-separated interchanges. Those with four or more lanes are divided by a median strip. Freeways in congested parts of large cities are often elevated (built above surface streets) or depressed (built below surface streets). The term freeway refers only to the free flow of traffic. Motorists may have to pay a toll to travel on these roads. Roads that require a toll are called tollways or toll roads.
Expressways are similar to freeways but sometimes have only partial access control. Parkways are roads resembling freeways. But they are built in parklike surroundings with attractive landscaping and scenery. Most parkways are limited to passenger vehicles.
Freeways and other roads are numbered to help travelers. In some countries, roads are designated by a combination of numbers and letters. In the United Kingdom, for example, freeways are designated by the letter M and a number, while minor roads begin with the letter B. The letters and numbers that represent the roads appear on road signs and on maps.
Signs on freeways and expressways alert drivers to exits and indicate the distance to the next rest area or service area with fuel and restaurant facilities. Emergency warning signs may be posted to tell drivers to slow down when approaching road construction or some type of hazard.
How roads and highways are built
Planning.
Highway planners study everything from the long-range needs of a region or an entire country to a particular section of a single route. This planning determines what the highway needs of the region are and how these needs can best be fulfilled and paid for.
Much road work involves improving existing roads. This may mean paving over a dirt road that is experiencing increasing traffic. New roads may be needed to cope with increasing traffic or to connect with a new town or development area.
In planning a system or a route, planners must learn: (1) where people live, (2) where they want to go, (3) by what means and route they get there, (4) where goods are produced, (5) what markets the goods are sent to, and (6) how the goods reach their final users. Traffic counts tell how many and what kinds of vehicles travel on a road, and when traffic is heaviest. From these and other facts about the past and present, planners try to predict future growth in population and industry, changes in land use, and how such growth and change will affect highway needs.
Public participation in road planning is essential. In many countries, planners hold public hearings on most major highway projects. These meetings enable citizens to present their views before a project begins.
Engineers have set standards for various kinds of roads, highways, and bridges. These standards govern the thickness and kind of foundation and surfacing for different kinds of traffic; the number of lanes needed; the sharpness of curves; and the steepness of hills.
Engineers run tests where a new road is to be built to find out how the soil’s properties differ when it is wet or dry. Such tests help determine the weight of traffic the road can support.
In planning a new road or rebuilding an existing one, maps must be drawn if they are not already available. These maps show the location of other roads, railroads, towns, farms, houses, and other buildings. They also show such natural features as rivers, lakes, forests, hills, and the slope of the land. Soil types may be identified.
Using these maps, engineers locate new highways and make drawings called plans, which show the boundaries of the right of way. The right of way is land needed for road pavement, shoulders, ditches, and side slopes. The plans also show the location, grades, and curves of the pavement, and the location of bridges and culverts.
In the United States, highway planners must also prepare an environmental impact statement before beginning construction. The purpose of such a statement is to discover in advance all the possible good and bad effects that a new highway may have on the public and on the environment.
Bypasses
are built to take motorists around cities. Motorists traveling some distance often do not want to drive through small towns or the centers of large cities that lie on their routes. Those traveling from one part of a city to another also usually prefer to avoid downtown traffic. The bypass helps these motorists avoid city traffic, and reduces traffic congestion for those who want to drive into town.
Bypasses are usually built as freeways, sometimes with service roads on one or both sides to serve local traffic. In large cities, a bypass may be called a circumferential or a beltway.
Intersections,
called junctions in some countries, are crossings of one road by another. Most intersections are at the same level, so that vehicles going east and west have to take turns crossing with vehicles going north and south. Sometimes roads intersect at odd angles, and it is especially difficult to make a safe crossing. At such places, the traffic engineer may put islands in the paved area to keep traffic in the proper paths. The best and safest kind of intersection is the grade—separated interchange. One common type of interchange is called a cloverleaf, because its curved inner ramps form the pattern of a four-leaf clover. A simpler kind is called a diamond because its ramps form that shape. Diamonds often connect a major highway and a secondary road. When two freeways intersect, more complex interchanges are sometimes needed. These may require a number of bridges and many ramps.
Grading.
The first job in building a new highway is to clear the right of way. There may be trees to cut down and stumps to pull up. Sometimes buildings must be torn down or moved. The right of way then is ready for rough grading. At this stage, huge machines called earth movers, which can dig up a roomful of dirt in one scoop, are used. They cut into the hills, carry the earth along, and drop it into the valleys to make a road with gentle grades. This method is known as cut-and-fill construction.
Sometimes, the right kind of earth to be used for the foundation of the road must be hauled in, perhaps from some distance away. While the grading is going on, culverts (pipes to carry away rain water) are put in place under the road or under driveway entrances. Ditches are cut at the roadsides to carry rain water to the culverts. After the right-of-way is shaped roughly for traffic lanes, shoulders, and ditches, it is smoothed and packed down to the required level and shape.
Paving
begins after grading is completed. The pavement is of definite thickness and is of stronger materials than the earth underneath. The kind and thickness of pavements depend largely on the weight and amount of traffic expected to use them.
In some places, different kinds of earth or soil are mixed together to form a pavement. Certain chemicals, lime, cement, or bitumens (asphalts and tars) may also be mixed with soil to act as a binder and to make it harder and more durable. On most of the low-traffic surfaced roads, however, the pavements are of gravel, crushed rock, or other mined materials. These types of pavements may be given a thin surfacing of bitumens known as seal coat.
Roads that carry heavy traffic must have a durable surface. An intermediate type of surfacing is called bituminous macadam. This is made by placing crushed stone or gravel on the roadbed, packing it down firmly, and filling the spaces with a bitumen. Better types of bituminous surfacing are made with sand, gravel, or crushed stone premixed with bitumens. These types of surfacing are laid with a paving machine, and then rolled hard and smooth. Bituminous pavement is sometimes referred to as blacktop.
Another hard surfacing material is portland cement concrete. It is made with sand, portland cement, water, and gravel or crushed stone. In both kinds of surfacing—bituminous and portland cement concrete—the aggregate (stone and sand) forms the body of the material and the bitumen or portland cement serves as a binder.
As roads are built, they are inspected continually, and tests are also made on the construction materials. After a road is finished, drilling machines take core samples of the paving and the base. Engineers use these samples to be sure that the finished paving is as thick and as strong as was planned.
Storm-water drainage.
Storm-water runoff from paved highways and parking lots may contain oil, exhaust emissions, and other dangerous chemicals from vehicles. These chemicals once mixed with storm water, enter rivers and streams. Many areas now require that highway projects include ditches or channels that direct storm water into temporary storage ponds. The water eventually evaporates or is absorbed into the ground. Storm-water storage facilities are also built near large parking areas.
Lighting.
Good lighting helps reduce the number of accidents for both vehicles and pedestrians. On most roads and highways, nearly all the light comes from the headlights of the trucks and cars. But on busy streets and at dangerous rural locations, overhead lights are used. Reflectors for the lamps are designed specifically to shine most of the light down on the roadway without glaring into the eyes of drivers.
Noise control.
The increased use of highways causes loud traffic noise, creating a problem for people who live nearby. For this reason, engineers have designed noise barriers made of concrete, wood, metal, plastic, and other materials that block sound. In some areas, trees, vegetation, or mounds of earth provide protection from traffic noise. Noise barriers are costly, but they successfully reduce highway noise in many areas.
Roadside improvement.
Roadsides are often planted with special grasses or vines to keep the earth from washing into the ditches. In addition, many roadsides are beautified with trees and bushes. Such planting and landscaping help break the monotony of travel and make the countryside more attractive. Many areas have laws that prohibit putting billboards and other commercial signs close to the road. Many highways have turnouts of various types where travelers can stop to picnic, to refuel, or to admire a scenic view.
How roads and highways are maintained
Repairing damage and resurfacing.
Roads and highways gradually wear out. The work of repairing and resurfacing is called maintenance. Maintenance also includes removing ice and snow, painting stripes on pavement, cutting grass, putting up signs, and caring for roadside shoulders, roadsides, and bridges.
Gravel and other similar type roads have to be smoothed quite often. Surfaces and edges of bituminous materials are repaired by patching with new material where worn spots develop from travel or because of weak spots in the ground underneath. Every 10 or 15 years, many roads with bituminous surfaces are resurfaced completely.
Workers repair concrete pavements by digging out broken sections and putting in new concrete. They often repair cracks by filling them with asphalt. Many older concrete pavements must be resurfaced completely.
Clearing ice and snow.
Most roads and highways must serve the year around. So roads in cold regions must be kept free from snow and ice in the winter. In some places, snow fences are put up. These are thin pickets wired together and placed parallel to the road, on the side from which the storm winds usually blow, and about 50 to 100 feet (15 to 30 meters) from the road. Snowdrifts then form between the fence and the road instead of piling up in the road.
Trucks with V-shaped or straight-blade plows attached to the front clear the roads when it snows. In deep drifts, special snowplows are needed. Some of the most powerful snowplows are called rotary plows. Rotary plows have a big screw at the front that chews into the snowdrifts and pulls the snow back into a large fan. The fan shoots the snow to one side of the road. Often roads and highways that are slippery from ice and snow must have salt, chemicals, sand, or cinders spread on them to keep them passable.
How roads and highways are paid for
Roads and highways are built and maintained by local and national governments.
In the United States,
local governments build and maintain most local and secondary roads, while state governments construct and care for primary highways. The federal government helps the states pay the cost of building and improving primary and secondary roads and streets. The routes are selected by the states.
State and local communities pay for roadbuilding and maintenance with tax receipts. Much of this money comes from taxes levied on highway and road users. Every state levies taxes on motor fuel and charges fees for registering motor vehicles. In some states, trucks and buses pay special fees. Some states levy a weight-distance or a ton-mile tax. This tax requires trucks to pay a set amount, based on the weight of the load and the distance it is carried.
Most highway-user taxes are spent only for roads and streets. Using this money for other purposes is called diversion. For example, some states set aside part of their motor fuel tax money for education. Constitutional amendments in many states prohibit such diversion.
Most states give part of the taxes they collect from highway users to local governments, to be spent on local roads. The local governments provide whatever additional money they need for roads, usually from general funds raised by property taxes.
State and local governments often borrow money to build roads. These loans, which are made by selling bonds, are repaid with tax money. Some state governments set aside part of their motor fuel tax money to repay these loans.
The cost of building many bridges and turnpikes (toll roads) is paid by the travelers who use them. Motorists pay a flat fee for crossing toll bridges. Fees for using turnpikes usually depend on how far the motorist travels. Large vehicles, such as trucks and trailers, usually pay more than passenger cars.
Since 1916, the federal government has aided states in building and improving the nation’s highways. This aid reflects the federal government’s interest in adequate roads for mail delivery, interstate commerce, national defense, and the general welfare of the country.
The federal-aid program was greatly expanded by legislation passed by Congress in 1956 and later years. Federal aid for primary and secondary roads and streets totals several billion dollars a year. The federal interstate highway system cost a total of about $120 billion over a period of about 40 years. The federal government paid 90 percent of the cost and the states 10 percent. To finance the interstate program, Congress established a highway trust fund. This fund receives money from taxes on motor fuel; tires; new trucks, trailers, and buses; and an annual tax on heavy vehicles. Construction or improvement of the roads is done by the states, with federal aid. The roads belong to the state or local governments, which must maintain them.
In other countries.
Road and highway construction and maintenance in industrialized countries are financed in ways similar to those in the United States. In the United Kingdom, the national and local governments work together on issues concerning road improvement. In Australia, a portion of a national gasoline tax, fees collected by the states for drivers’ licenses, and local property taxes all contribute to the funding for road construction and development.
In less developed countries, funds for road construction may come from a development budget that is part of a country’s total annual budget. The total budget is supported by customs duties, sales taxes, taxes on mined resources, and other revenues. Foreign investors often pay for the construction of roads in areas in which they operate businesses.
History of roads and highways
The first roads.
Because roads are so old, experts are unsure of the origin of the word road. Most think it came from the Middle English word rode, meaning a mounted journey. This may have come from the Old English rad, from the word ridan, meaning to ride.
In England, hundreds of years ago, certain main roads were higher than the surrounding ground. This was because earth was thrown from the side ditches toward the center. Because they were higher, they were called highways. These roads were under protection of the king’s men and were open to all travelers. Private roads were known as byways.
The first roads in the world probably followed trails and paths made by animals. These trails and paths led from feeding grounds to watering places. People followed these trails to hunt for animals. People also made their own trails and paths in searching for water, food, and fuel. Explorers followed these trails as they investigated new lands.
Early roads were built in the Near East about 3000 B.C., soon after the wheel was invented. As trade developed between villages, towns, and cities, other paths, or trade routes, were made. One such early system of roads was the Silk Road, which ran about 5,000 miles (8,050 kilometers), connecting China with Europe. Merchants used this ancient route to carry Chinese silk across Turkestan, India, and Persia.
The first road markers were piles of stones at intervals. Trails through forests were marked by blazing trees, or cutting a piece from the bark of the tree.
The Egyptians, Carthaginians, and Etruscans all built roads. But the first really great road builders were the Romans. They laid a solid base and gave the road a pavement of flat stones. The Romans knew that the road must slope slightly from the center toward both sides to drain off water. This gave the road a crown. The Roman road builders knew also that there must be ditches along the sides of the road to carry water away. Roman roads were built to assist in the movement of soldiers and for communication and trade throughout the Roman Empire. These roads ran in almost straight lines and passed over hills instead of cutting around them. The Romans built more than 50,000 miles (80,000 kilometers) of roads in their empire and some of them still are in use.
From the 500’s to the 1800’s,
most roads in Europe were merely clearings in the forests. Cobblestone paving was used in some urban areas. There was little reason to build good roads, because most of the travel was on horseback. The cleared way was sometimes quite wide, so that robbers hiding in the woods could not leap out suddenly upon unsuspecting travelers.
In South America, from the 1200’s to the 1500’s, the Inca Indians built a network of 10,000 miles (16,000 kilometers) of roads. The roads connected their cities.
The first highway department was established in France in 1716. This department built Europe’s finest gravel and stone roads of the 1700’s using methods developed by Pierre M. J. Tresaguet, an engineer.
In the early 1800’s, the person who did more for European roadbuilding than anyone else up to that time was John Loudon McAdam, a Scottish engineer. McAdam is remembered for the surface he developed for roads. This kind of surface, called macadam, is still used today. McAdam also stressed the importance of proper drainage to keep roads on a solid foundation.
Early American roads.
The first settlers in North America found a wilderness. They located their homes along the rivers and bays and used the water for transportation. As new settlers went inland, they usually built crude roads to the nearest wharf. Until after the War of 1812, people traveled mainly on foot or on horseback.
The first extensive hard-surfaced road was completed in 1794. This road was called the Lancaster (Pennsylvania) Turnpike. It measured 62 miles (100 kilometers) long and was surfaced with hand-broken stone and gravel. In the next 40 years, many turnpikes were built. Most surfaces were of earth, gravel, or broken stone. Some roads were covered with logs or planks, laid crosswise. Where logs were used, the roads were called corduroy roads. Both corduroy roads and plank roads were very bumpy.
In 1830, the steam locomotive was successfully operated and rapid development of railroads began. Many people became convinced that the railroad was the best means for travel over long distances. From 1830 to 1900, there was little change in the surfacing materials for roads and highways.
Modern roads.
By 1900, there was a growing demand for good roads. Roads that extended a short distance were built in the United States to give farmers access to the railroads, which hauled farm products. The first freeway was completed in 1921 in the Grunewald, a forest area in Berlin, Germany. This road, which was 6 miles (10 kilometers) long, served as a route for suburban commuters and as a race track. Italy soon began building freeways. In 1925, the United States adopted its system of numbering highways, which was suggested by Wisconsin highway engineer A. R. Hirst in 1917.
In 1934, Germany began building its Autobahn (expressway) system. This extensive system featured divided highways, grade-separated interchanges, and well-designed service areas. A section of the Pennsylvania Turnpike, the first U.S. freeway, opened in 1940. This section ran from Middlesex (near Carlisle) to Irwin. In California, the Arroyo Seco Parkway opened in 1940 between Pasadena and Los Angeles. This and similar roads opened new suburban areas to development, and population often grew quickly where freeways were built. Few other highways were built from the Great Depression of the 1930’s until the end of World War II in 1945. After the war, road construction in industrialized countries increased, as more and more families purchased automobiles.
In the 1950’s, many United States industry and civic groups joined in supporting highway improvement programs. The major work on the U.S. federal interstate highway system began in 1956. This system became part of the National Highway System in 1995.
The governments of many of the developing nations of Africa and Asia have begun modernization and industrialization programs that include the building of new roads. Industrialized nations continue to improve and expand their road systems. Engineers today continue to seek ways of increasing highway safety through better construction. They also seek to improve traffic flow by using computers to help plan road systems.
