John Loudon McAdam - Legacy

Inventor of macadamized roads, born in Ayr, South Ayrshire, SW Scotland, UK. He went to New York City in 1770, where he made a fortune in his uncle's counting-house. On his return in 1783 he bought an estate and started experimenting with new methods of road construction. In 1816 he was appointed surveyor to the Bristol Turnpike Trust, re-made the roads there with crushed stone bound with gravel, and raised the carriageway to improve drainage. In 1827 he was made surveyor-general of metropolitan roads in Great Britain, and his macadam surfaces were adopted in many other countries.

He invented a new process, "macadamisation", for building roads with a smooth hard surface that would be more durable and less muddy than soil-based tracks. He returned to Scotland in 1783 and purchased an estate at Sauchrie, Ayrshire.yup

His experiences trying to manage and move about his estate prompted him to consider and research how road construction might be improved. McAdam had also been 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 "macadamization", or, more simply, "macadam". The first macadam road in North America, the National Road, was completed in the 1830s and most of the main roads in Europe were macadamized by the end of the nineteenth century.

Although McAdam was paid £5,000 for his Bristol Turnpike Trust work and made "Surveyor-General of Metropolitan Roads" in 1827, professional jealousy cut a £5,000 grant for expenses from the Parliament of the United Kingdom to £2,000 in 1820. His efficient road-building and management work had revealed the corruption and abuse of road tolls by unscrupulous Turnpike Trusts, many of which were run at a deliberate loss despite high toll receipts.

Legacy

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) – followed later by the use of hot-laid tarred aggregate or tar-sprayed chippings to create better road metalling. More recently, oil-based asphalt laid on reinforced concrete has become a major road surface, but its use of granite or limestone chippings still recalls McAdam's innovation.