John Loudon McAdam Changed Roads Forever

John Loudon McAdam. Three Lions / Hulton Archive / Getty Images

John Loudon McAdam was a Scottish engineer who modernized the way we build roads.

Early Life

McAdam was born in Scotland in 1756 but moved to New York in 1790 to make his fortune. Arriving at the dawn of the Revolutionary War, he began working in his uncle’s business and became a successful merchant and prize agent (in essence, a fence who takes a cut from selling off the spoils of war). 

Returning to Scotland, he purchased his own estate and soon became involved in the maintenance and governance of Ayrshire, becoming a road trustee there.

Builder of Roads

At the time, roads were either dirt paths susceptible to rain and mud, or very expensive stone affairs that frequently broke down not long after whatever event precipitated their construction. 

McAdam was convinced that massive stone slabs would not be needed to carry the weight of passing carriages, as long as the road was kept dry. McAdam came up with the idea of raising roadbeds to ensure adequate drainage. He then designed these roadbeds using broken stones laid in symmetrical, tight patterns and covered with small stones to create a hard surface. McAdam discovered that the best stone or gravel for road surfacing had to be broken or crushed, and then graded to a constant size of chippings. McAdam's design, called "MacAdam roads" and then simply “macadam roads,” represented a revolutionary advancement in road construction at the time.

The water-bound macadam roads were the forerunners of the tar- and bitumen-based binding that was to become tarmacadam.

The word tarmacadam was shortened to the now-familiar name: tarmac. The first tarmac road to be laid was in Paris in 1854, a precursor to today's asphalt roads.

By making roads both significantly cheaper and more durable, MacAdam triggered an explosion in municipal connective tissue, with roads sprawling out across the countryside.

Fittingly for an inventor who made his fortune in the Revolutionary War—and whose life’s work united so many—one of the earliest macadam roads in America was used to bring together the negotiating parties for the surrender treaty at the end of the Civil War. These reliable roads would be crucial in America once the automobile revolution began in the early 20th century.