The history of tarmacadam roads

How an accidental spillage and a sharp-eyed surveyor led to a modern road surface

In 1901, Edgar Purnell Hooley, a surveyor for Nottinghamshire County, was strolling around Denby in Derbyshire, England. As part of his role, he was required to carry out odd jobs throughout the county. But on one particular day, he came across an unusually smooth piece of the road while passing a factory.

At the time, roads were just chipped pieces of small gravel, meaning that they quickly deteriorated as large ruts from wheels became embedded in them. The road became difficult to pass due to large amounts of dust, and sharp bits of stone able to puncture tyres.

By 1820, a Scottish engineer by the name of John Loudon McAdam had created a basic road surface, but he had never found a way to stick the stones together.The section of road Hooley was investigating looked remarkably pristine. He spoke with locals and learned that a barrel of tar had burst open across the road.

In efforts to reduce the mess created by the sticky substance, a quick-thinking employee had dumped waste slag from a nearby ironworks on top of the tar.

This improvised resurfacing of the road had solidified and smoothed the track, inadvertently leading to the development of the modern tarmac road. The following year, Hooley patented the process of heating tar and then mixing it with slag and broken stones. This new, hardwearing road surface was successfully marketed as tarmacadam in honour of its original inventor. Once the recipe was perfected, Nottingham’s Radcliffe Road became the first tarmac road in the world.

This article was originally published in How It Works issue 112, written by Charlie Evans

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