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John Loudon McAdam

pioneer road builder

John Loudon McAdam

John Loudon McAdam was born in Ayr, Scotland, on September 21, 1756. Upon the death of his father in 1770, John was sent to New York in the care of an uncle, a merchant. John also became a merchant, and by the mid-1770s his business prospered from Boston to Charleston. Aligning himself with the loyalist side during the Revolutionary War, McAdam served in the British reserves and was a government contractor engaged in the sale of war prizes arising out of the War. After the war, John and his family were no longer welcome in America and they returned to Scotland in 1783, leaving much of his wealth behind.

Buying an estate near Maybole, McAdam soon acquired an interest in the local iron works and mills that manufactured coal products. During this period he also began working on the concept for which he is now best known -- the macadamized road surface.

McAdam's first experiments at building a road were conducted when he had a road built from the Alloway-Maybole Highway to his estate. During the process he experimented with a variety of road-building stones and road-making techniques until he was satisfied with the result. The road he built eventually became the highway, which was still in use into the 1930's.

In 1801, McAdam was named to the post of Surveyor General to the city of Bristol. The roads surrounding Bristol, then a rapidly growing port, were in a bad state of disrepair. McAdam drew up a specification for a road bed raised slightly above the level of the surrounding land to facilitate drainage. Drainage ditches edged each side, and the road itself consisted of large pieces of crushed rock laid compactly. The road was 18 feet wide and the crown in the middle rose 3 inches. The surface layer consisted of broken angular pieces of granite or greenstone -- no piece heaver than 6 ounces. Successive layers of stone were then laid as each preceding surface was compressed by the traffic. In this way, under pressure, the surface became virtually self-sealing.

McAdam described his methods in two books: Remarks on the Present System of Road-Making (1816) and Practical Essays on the Scientific Repair and Preservation of Roads (1819).

The practical advantages of McAdam's road soon became quite obvious, and a parliamentary inquiry into road building in 1823 led to McAdam's system being officially adopted. In 1827, he was made Surveyor General of Roads in Britain. His method was also quickly adopted in other countries, notably in the United States. It introduced the verb "macadamize" into the English language, and remained the standard method of road construction until the development of the automobile, whose rubber tires tore the small stones out of their bedding. This made necessary the use of a new, "tar macadam," and ultimately a further revolution in road engineering.

McAdam held valid patents on his method of road building that he had developed, undertaken, and built at his own expense. His methods proved so important, however, that his patents were not protected and enforced by the government. Parliament eventually awarded him some payment, but he was never fully compensated for his work nor did he ever receive royalties for use of his method. Towards the end of his life he was offered a knighthood for his work, but turned it down due to his advanced age.

John Loudon McAdam died on November 26, 1836.

Feldman, Anthony and Peter Ford Scientists and Inventors, The People Who Made Technology from Earliest Times to Present Day New York: Facts on File, 1979

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This page was last updated on March 07, 2017.