McAdam, John Loudon (1756–1836)

Scottish engineer, inventor of the macadam road surface. It originally consisted of broken granite bound together with slag or gravel, raised for drainage. Today, it is bound with tar or asphalt.

McAdam introduced a method of road building that raised the road above the surrounding terrain, compounding a surface of small stones bound with gravel on a firm base of large stones.

A camber, making the road slightly convex in section, ensured that rainwater rapidly drained off the road and did not penetrate the foundation. By the end of the 19th century, most of the main roads in Europe were built in this way.

McAdam was born in Ayr. Emigrating to the USA at 14, he returned to the UK in 1783. He was appointed paving commissioner in Bristol in 1806; ten years later he became surveyor-general of the roads in that region, and of all the roads in Britain in 1827.

McAdam was also responsible for reforms in road administration, and advised many turnpike trusts. He ensured that public roads became the responsibility of the government, financed out of taxes for the benefit of everyone.