Macadam

Macadam, road-building system devised by the Scots engineer John Loudon McAdam (1756–1836). The soil beneath the road, rather than foundations, bears the weight, the road being waterproof and well-drained to keep this soil dry. For modern highways a first layer of larger rocks is laid, then smaller rocks and gravel; the whole is bound with (usually) asphalt or tar.

See also: McAdam, John Loudon.