Portal:Scotland/Selected article/Week 33, 2016

John Loudon McAdam (21 September 1756 – 26 November 1836) was a Scottish engineer and road-builder. He invented a new process, "macadamisation", for building roads with a smooth hard surface, using controlled materials of mixed particle size and predetermined structure, that would be more durable and less muddy than soil-based tracks. McAdam was born in Ayr, Scotland. He was the youngest of ten children and second son of the Baron of Waterhead. The family name was traditionally called McGregor, but was changed to McAdam (claiming descent from the Biblical Adam) for political reasons in James I's reign. He moved to New York in 1770 and, as a merchant and prize agent during the American Revolution, made his fortune working at his uncle's counting house. He returned to Scotland in 1783 and purchased an estate at Sauchrie, Ayrshire.

McAdam was appointed surveyor to the Bristol Turnpike Trust in 1816, where he decided to remake the roads under his care with crushed stone bound with gravel on a firm base of large stones. A camber, making the road slightly convex, ensured rainwater rapidly drained off the road rather than penetrate and damage the road's foundations. This construction method, the greatest advance in road construction since Roman times, became known as "macadamisation", or, more simply, "macadam". The macadam method spread very quickly across the world. The first macadam road in North America, the National Road, was completed in the 1830s and most of the main roads in Europe were subject to the McAdam process by the end of the nineteenth century. Modern road construction still reflects McAdam's influence. Of subsequent improvements, the most significant was the introduction of tar (originally coal tar) to bind the road surface's stones together, "tarmac" (for Tar Macadam).