McAdam, John Loudoun (1756–1836). Road surveyor. Returning as a loyalist from New York in 1783, McAdam settled in Ayrshire, and managed the British Tar Company; selling his modest estate in 1795 to discharge debt, he re-emerged at Falmouth from 1798 as a naval prize-monger. His travels turned interest into profession, as he covered nearly 19,000 miles in 1,900 days on the road, 1798–1814, making the observations that formed his ‘principles’: employing small stones direct onto the subsoil as the method of making effective roads largely impermeable to water. These were presented to the House of Commons in 1811, and further observations (1819–20) came in dispute with Telford, whose roads proved more durable but expensive. McAdam secured appointment as surveyor-general of the Bristol roads from 1816, and unpopularly consolidated his dynasty across Britain: McAdam, three sons, four grandsons, and a brother-in-law held 136 surveyorships in England and 8 in Scotland, 1816–61, with a total of around 3,700 miles of turnpike road. His fame led to the use of the term ‘macadamize’ as early as 1824, and was revived in Hooley's patent Tar Macadam (1901).

J. A. Chartres

McAdam, John Loudon (1756–1836) Scottish engineer who invented the macadam road surface. McAdam proposed that roads should be raised above the surrounding ground, with a base of large stones covered with smaller stones and bound together with fine gravel. He was made surveyor general of roads in Britain in 1827.