With the fall of the Roman Empire in the fourth century A.D., the art of road building suffered a decline for fourteen hundred years. It was the eighteenth century before engineers turned their attention to making roads safe and easy to travel. One of the leaders spearheading the road-building revival was John McAdam. Born in Ayr, Scotland, McAdam went to the American colonies at the age of fourteen, after the death of his father. There he was a salesman of property seized during military battles.
McAdam returned to Scotland in 1783 and remained in government employ for the remainder of his life. In his initial post, deputy lieutenant of Ayrshire and a road trustee, McAdam spent his own money experimenting with road construction methods. In 1789 he became a navy food supplier and in 1803 went to work for the Board of Works in Bristol, England. He was named Bristol's surveyor-general of the Roads Trust in 1815, moving in 1827 into the post of general surveyor of metropolitan roads for Great Britain.
McAdam's philosophy of road building was that the natural roadbed and its subsoil were sufficient as a road foundation. He advocated using crushed stone or granite chips, well-drained via grading and compacting. If three or four layers of broken stones were laid, water--a constant presence in the British Isles--could be absorbed into the road without affecting its load-carrying ability. He discounted a suggestion by Richard Edgeworth (1744-1817) that road surfaces could be rendered even more waterproof by using sand between the stones.
McAdam's technique was much more economical than the foundation-building methods of Pierre Trésaguet and Thomas Telford, and eventually supplanted them. The invention of the steamroller in 1866 made McAdam's method even more effective. Today, the term macadam refers to any road having a simple, compacted bed, considered to be the perfect type of road.
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