Macadam is a type of road construction which relied on layers of crushed rock. It was developed around 1820 by Scottish engineer, John Loudon McAdam who was the trustee of the Ayrshire Turnpike in Scotland. His interest in paving moved from a hobby to an obsession, and eventually led him to Bristol where he was responsible for 149 miles of road.
Observing existing paving methods, Loudon used a combination of small pieces of rock and rock dust to form a relatively smooth surface which was simple to build yet surprisingly durable. Some of his ideas would strike modern day people as peculiar, such as his belief that stones must be uniform and shaped by hand.
With the advent of the automobile, speeding cars became a serious problem on macadam roads, sucking dust from the road’s surface, reducing visibility and undermining its structure. This problem was solved by spraying a thin layer of tar to bind dust and stone together creating tar-macadam, a precursor to modern day asphalt.