Curbstone Presents - the American Road

Painting by Carl Rakeman

The first macadam surface in the United States was laid on the "Boonsborough Turnpike Road" between Hagerstown and Boonsboro, Maryland. By 1822, this section was the last unimproved gap in the great road leading from Baltimore on the Chesapeake Bay to Wheeling on the Ohio River. Stagecoaches using the road in winter needed 5 to 7 hours of travel to cover 10 miles.

Construction specifications for the turnpike road incorporated those set forth by John Loudon McAdam of Scotland. After side ditches were dug, large rocks were picked and raked, then were broken "so as not to exceed 6 ounces in weight or to pass a two-inch ring." Compacting work for each of the three layers was quickened using a cast-iron roller, instead of allowing for compacting under traffic.

In 1830, after 5 years of work, the 73-mile National Pike (or Cumberland Road) became the second American road to be built on the "McAdam principle."

The wearing surface of a road, street, or sidewalk. Parts of Babylon and Troy are believed to have been paved; Roman roads were noted for their durable stone paving. Roman empire city streets were normally paved with "basalt slabs". The elevated sidewalks that were generally built on both sides of the street often took up as much as half of the total street width and were paved with "peperino stone". Streets outside of the city proper were also paved as well, or at the very least had a gravel surface.

The first road to be paved with asphalt was in Babylon between 625 and 604 B.C. The Romans built an impressive road system in Great Britain during their occupation of the first through fourth centuries, of which many roads have been used as templates for modern British roadways.

Credit for modern road construction goes to the Roman Army, their military road building techniques are the prototype for the roads of today. Roman city streets, with their curbstones and elevated sidewalks are the basis for the modern street designs that we see today.

Early roads in the United States were simply ruts carved into the ground by the many horses and wagons that traversed across this great land. Travel was brutal at best, add to that any inclement weather conditions and you get the picture. Cobblestones were common from late medieval times into the 19th cent.

In 1876, President Grant selected a group of army engineers to study the use of asphalt on roads. This group suggested that Pennsylvania Avenue in Washington, D.C., be paved with sheet asphalt made from Trinidad Lake asphalt. That pavement remained in excellent condition for 11 years, despite the traffic at the White House.

Historic Pennsylvania Ave. was first paved with asphalt in 1876. In this photo, taken in 1907, crews repave with the equipment of the time.

Desirable qualities in pavements include durability, smoothness, quietness, ease of cleaning, and a nonslippery surface. The requirements conflict to a degree, so no one material is ideal in all respects. The foundation of a pavement must be crowned, or slightly arched, for rapid shedding of water; it must be strong enough to withstand heavy dynamic loads, but capable of responding to temperature changes. It has been estimated that some 27,000 tons of water fall annually on one mile of road.

Early in the 19th century, rock asphalt and natural asphalt were being used as building products. These asphalt products had already been used for the past 7,000 years for waterproofing. Hot tar was used in England as early as 1820 to bind the broken stones together. This type of mix, known as tarmacadam, was patented in 1910 by Warren Brothers in Cambridge, Mass. This company later became APAC, one of the largest asphalt mix companies in the United States.
The highway builders of the late 1800s depended solely on stone, gravel and sand for road construction. Road surfaces could be stabilized by adding water to the surface sand to form a binder, which would support horsedrawn traffic. Mud and dust did not become a major problem until the introduction of the automobile.

In 1919, the Washington-Richmond Road near Dumfries, Va., about 30 miles (48 km) south of Washington, D.C., claimed this car. Mud was a serious problem before asphalt paving.

The deplorable conditions of the nations roads became a great public concern in the late nineteenth century with the invention of the bicycle and later the motor car. In the early 1890's bicycle clubs in the United States pushed hard for road improvements. These efforts brought about the "National League for Good Roads" in 1892. Continued dissatisfaction with the conditions of the nations roads resulted in the creation of the "Office of Road Inquiry" by Congress in 1893.

As the cities and nations continued to grow and expand, a more cost effective way of building streets was needed. The complete implementation of asphalt on roads, however, began with a man named John Metcalfe.
Metcalfe was born in Scotland in 1717. Although blind from the age of six, Metcalfe built 180 miles of roads in Yorkshire, England, after the age of 40. He made sure that his roads drained well and were built on a firm foundation. He built them with three layers: the first layer was made up of large stones, the second contained excavated road material, and the third was a layer of gravel. The road was also arched in the center so that water would drain off and down into the ditches built along each side.

Thomas Telford, who was born in Eskdale, Scotland, in 1757, perfected the method of building roads with broken stones. Telford placed the stones at a certain thickness in accordance with the weight and volume of traffic on that road. He also took into consideration road alignment and gradient, which are still important factors for roadbuilders today.

John Loudon McAdam (1756-1836)

Engraving by Charles Turner. By courtesy of the trustees of the British Museum; photograph, J.R. Freeman & Co. Ltd.

John Loudon McAdam, born in Scotland in 1757, and the general surveyor for the city of Bristol, England, designed roads using broken stones that were laid evenly and tightly so that they covered the soil and formed a hard surface. These “macadam roads,” as they were called, served the purpose of providing a somewhat stable pathway for pedestrians and horsedrawn traffic.

While Telford and McAdam were contemporaries, they each had different ideas of how to build the best road. Telford’s designs were more expensive than McAdam’s, but some scholars say they were superior in quality.

Macadam construction diagram.

Macadam consists basically of compacted layers of small stones cemented into a hard surface by means of stone dust and water (water-bound macadam). However, the main pavement surfaces in use today are bituminous/asphalt coverings and concrete.

The macadam method of road building uses a layer of well drained and compacted subsoil to support the load weight of the roadway, while the top layer acts as a wearing surface built only to shed water. Modern day macadam road construction is based on this practice and is used worldwide.

The top layer of a macadam road is mostly made of asphalt and rocks, now some builders use other ingredients to help deter road wear and add traction to the surface. Nowadays asphalt is made synthetically, but true asphalt in its natural state was originally found in only one place in the world, in a pitch lake on Trinidad Island.

Sir Walter Raleigh, in his third voyage in 1498, discovered the still-famous pitch lake of asphalt on the Island of Trinidad, the largest natural asphalt lake in the world. "Trinidad Asphalt" as it was known, was much prefered over the manmade variety, because it had a good record for standing up to time and the elements. Trinidad was the first source of asphalt made available in America; the second source was the Bermudez Lake in Venezuela.

Macadam construction with asphalt.

By 1910, refined petroleum asphalt had gained its permanent market supremacy over the producers of rock, natural and sheet asphalt. The oil companies could manufacture asphalt superior to that mined from the natural deposits in Trinidad Lake and Bermudez Lake. This supremacy even threatened diplomatic relations between the United States and Venezuela.

In the bituminous macadam pavement, the foundation is macadam, upon which a bituminous material that penetrates at least 2 in (5 cm) into the foundation is poured, forming an impervious binder. In the bituminous-mixed macadam pavement, a mixture of crushed rock, ground glass and other additives, and bituminous binder is spread over a macadam foundation and rolled into a compact mass.

Key Dates of Interest in United States Road Building
1625 - Earliest known paved American road - Colonial city street - Pemaquid, Maine
1795 - First engineered American road - Philadelphia to Lancaster toll turnpikee
1823 - First macadam road constructed in America - State of Marylande
1877 - First asphalt paving in N. America - Pennsylvania Avenue - Washington, DC
1893 - First rural brick road - Ohioe
1906 - First Bituminous macadam road constructed - Rhode Islande

The two other pavement types use a concrete road slab as a foundation. In the sheet asphalt pavement, a binder course and a wearing course are laid over a concrete foundation. The binder course, whose function is to prevent creepage of the upper course, is composed of broken stone and asphalt cement. The wearing surface is a mixture of fine sand, filler, and asphalt.

By far the most common type of pavement for heavy use is rigid concrete. The first concrete pavement was laid in Bellefontaine, Ohio, in 1894. A modern highway will have a 6 in (15 cm) base of concrete, on top of which 3 in (7.5 cm) of steel-reinforced concrete will be laid. Pavements that must withstand only pedestrian traffic may use brick or wood-blocks, set in a 1 in. (2.5 cm) bedding of sand, cement mortar, or mastic.

1910 - Spreading asphalt Macadam on crushed rock base, State Aid Road No.59 - 85, Yakima County. Washington State.

1912 - Steam roller compacting macadam. Washington State.

1910 - Auto-truck spreading asphalt Macadam, Walla Walla County, Washington State.

1911 - Crushing plant and hauling machinery used in building permanent highway, Yakima County. Washington State.

The U.S. Corps of Engineers, which had not previously been involved in pavement matters prior to World War II, was charged with military road and runway construction. Faced with the production of larger, heavier airplanes, the Corps needed to come up with pavement thickness design methods for runways that could handle wheel loads greater than 12,500 pounds (5,670 kg). Not only did they meet the huge military demand for heavy-duty pavements, but they would continue to influence all aspects of asphalt paving long after the war was over.

In 1956, the Federal- Aid Highway Act was established, creating an infrastructure highway program unmatched by any other in the world. President Dwight D. Eisenhower stated that the Interstate System would establish “a grand plan for the rebuilding of our obsolete road and street system.” The basis of the system was a 41,000-mile (65,983-km) highway network connecting major cities in the Unites States. One component of this plan was that for every five miles of road, one mile would be straight for use as an airplane landing strip in time of need.

The network design task was given to the U.S. Bureau of Public Roads and the State Highway Departments. While many state highway departments requested asphalt for their part of the interstate system, concrete was also used despite its higher cost of construction.

Besides cost, another feature that makes asphalt superior to concrete is flexibility. Maintaining asphalt is also typically less expensive than maintaining concrete.