John Loudon McAdam changed the world of road building forever. 

John Loudon McAdam. Source: Stephencdickson/Wikimedia

John Loudon McAdam was a pioneering Scottish engineer who almost single-handedly changed the way roads were built around the world. His innovative shallow camber, crushed, compacted stone layered roads would become the standard for road building throughout the world. 

His road-building innovation is today widely considered the biggest advancement in road building since the Roman Empire.

Not only did McAdam's design result in a smoother surface and carriage ride, but it was cheaper to build and lasted longer. This 'new' roadway surface and construction process have since been immortalised with McAdam’s name, often with the Americanised spelling 'MacAdam' or 'macadam'.

The advent of motor vehicles has meant many of the original roads have now been resurfaced or replaced with a tar coating or asphalt. However, if you are lucky, you might still see some surviving examples of his original roads around the world today. 

McAdam's life was interesting in and of itself. Born into aristocracy, family problems would see him move to the US just before the American War of Independence. After the conclusion of the war, he and his family would return to the UK to restart their lives once again.

An illustrious career in road building would follow, eventually, seeing him invent one of the most important advancements in civil engineering of the age. 

Early life

McAdam was born in Ayr, Scotland, on September 21, 1756. His father was James McAdam, Baron of Waterhead, and his mother was Susanna Cochrane, the niece of the seventh Earl of Dundonald. He was the youngest of 10 children and the second son of the Baron of Waterhead.

His elder brother, James, a captain in the military, died when McAdam was about seven years old. It is not clear if he died of natural causes or from his services in the army. This tragic event left him as the only surviving male within the Waterhead family line. 

Interestingly, his family name is thought to have changed from McGregor at some point in their ancestry. This is thought to have been changed to McAdam sometime during King James VI's reign, possibly for political reasons. The name change is a direct reference to the claim of descent of the family from the biblical Adam, 'Son of Adam'. 

McAdam's family stayed in the house he was born until 1760 when a new residence was built in Lagwyne. Now a ruin, Lagwyne Castle, was located on the outskirts of Carspairn in Scotland. This was part of the Waterhead Estate. 

Shortly after moving in, the castle actually burnt down. McAdam's parents were away on business when the tragedy occurred, and John narrowly escaped the flames when he was rescued by the family nurse.

The currently standing Blairquhan Castle in Ayrshire, Scotland. Source: Blairquhan Castle

His father decided not to rebuild the castle and moved his family to another castle in Blairquhan, near Straiton, owned by the Whiteford family. Called Whitefoord Castle, this castle has since itself been demolished and replaced with the current standing Blairquhan Castle.

Moves to America to make his fortune

His father had somewhat of a less than ordered lifestyle and poorly managed his financial affairs. Almost inevitably, this lead to his father's financial ruin as his company, the Bank of Ayr, went bankrupt. The resulting financial devastation forced his father to sell his family's ancient Waterhead estate. 

His early life went from bad to worse when his father passed away when John McAdam was only 14. His family thought it best that the young McAdam be sent to America in 1770, to be looked after by his uncle, William MacAdam, who was a successful New York merchant.

Under his wing, McAdam learned the ropes of his uncle's business. and also helped his uncle found the New York Chamber of Commerce. Notable members included none other than Samuel Adams and Paul Revere.

McAdam, clearly inspired by his uncle, quickly became a merchant in his own right. His business prospered, and he even co-financed a privateering ship, General Matthew, which was engaged in the battle of Savannah Harbor during the Revolutionary War. The vessel was heavily damaged during the conflict by the American patriot forces. 

McAdam would later marry Gloriana Nicoll, the daughter of William Nicoll of Suffolk, New York. The couple inherited one-third of West Neck on Shelter Island and Blue Point Islip. When the American War of Independence began, McAdam and his extended family declared their support for the loyalist forces – a decision they would soon come to regret.

Source: Rikki/Julies Reque/Flickr

The family's support would go further than declared loyalty, with his uncle becoming an 'Aide to Camp' to Adjutant General Richard Maitland of the British forces in America. Maitland later married Mary McAdam, John McAdam's aunt.

McAdam himself served in the British reserves during the revolution and also acted as a government contractor and engaged in the sale of prizes of war.

Returns to UK

As you can imagine, once the American War of Independence was concluded, McAdam and his family were no longer welcome in America. McAdam, his wife, and their two children, swiftly relocated to Scotland in 1783. John's substantial assets in America were subsequently 'appropriated' by the new American government, but he did manage to take enough of his wealth with him to purchase an estate in Sauchrie, Ayrshire.

Once settled, McAdam took part in some local affairs in Ayrshire including operating the local Kaims Colliery. This coal mine supplied coal to the British Tar Company of Admiral Archibald Cochrane ninth Earl of Dundonald and Partners. 

His association with Admiral Lord Cochrane enabled him to acquire an interest in the ironworks and mills of the area that produced coal products, including tar. 

The steel manufacturing processes, in particular, had a need for the coke byproducts from processing coal. At this time, the flammability of coal gas was not recognised, and sadly for the earl, this was not capitalised on.

Example of a 'Macadam Road' in about 1850. Source: Sutter County Library/Wikimedia

Cochrane had ambitions to sell the tar to the Royal Navy as a sealant for their ship's hulls. Tests were conducted on a buoy which was very encouraging for both Cochrane and the navy. The use of tar as a sealant was greatly reduced, however, when ships began to use copper sheathing instead. Cochrane's investment in tar had proved disastrous for him personally.

For McAdam however, this experience had, given him a strong knowledge base for his later revolutionary invention. 

Laying the foundations for macadam roads

Soon after his return to the UK, McAdam had also begun to experiment with road construction. One of his first tests was with road stones. He successfully built a road leading from the Alloway-Maybole highway to his newly acquired estate. 

His road eventually became part of the highway and, interestingly enough, it was still in use right up to 1936. 

In 1787, McAdam became a trustee for the Ayrshire Turnpike. He found himself becoming increasingly involved over time with the day-to-day maintenance and construction of roads over the next decade. 

In 1794, McAdam accepted his commission as a Major in the Royal Artillery Corp. He was particularly proud of this achievement, which incidentally, was one of the last to be personally signed by King George III. In 1798 he also received a government appointment during the early stages of the Napoleonic War.

His role was as an agent providing logistical support for the Royal Navy in Falmouth, England. In 1801 he was recommended for a post as a surveyor at the Bristol Turnpike. 

Ayr, Scotland. Source: Billy McCrorie/Wikimedia

McAdam accepted the position, and this one decision that would change his life and the world of roads as we know it forever. 

Roads would never be the same again

After deciding to move to Bristol in 1802, he became a general surveyor for the Bristol Corporation in 1804. His experience with road construction over the last few years began to crystallise McAdam's ideas for a huge improvement to the way roads were constructed. 

By this time he was a trustee for no less than 34 road trusts. McAdam would put forward several cases for parliamentary consideration on improving current infrastructure with a then-novel solution. On three separate occasions in 1810, 1819, and 1823 he provided evidence for parliamentary inquiries. He also penned two treatises in 1816 and 1819.

McAdam starts to make waves

Around this time, McAdam began to formalise his ideas by putting pen to paper. In his Remarks on the Present System of Road-Making and Practical Essay on the Scientific Repair and Preservation of Roads, He argued that roads should be raised above the surrounding ground. He also argued that they should have a composite structure of layered rocks and gravel laid in a systematic process.

At around this time, in 1816, McAdam was appointed as a dedicated surveyor for the Bristol Turnpike Trust. Putting his "money where his mouth is" McAdam began to remake the roads using crushed stone bound with gravel built on a firm base of foundation stones.

A Macadam-style road in Huntingdon County, PA. Source: Shari Weinsheimer/Wikimedia

His new roads also had a camber, which made them ever so slightly convex. This ensured rainwater could rapidly drain the carriageway instead of pooling and penetrate the structure. This has been recognised by many as the greatest advance in road building since the Romans almost 2000 years before. 

The process would later come to be known as Macadamisation, or simply Macadam roads.

The Macadam road is born

McAdam's new roads quickly became popular around the world. The National Road in the United States, completed in 1934, was one of the first Macadam roads in North America. His process quickly took Europe by storm as well, with the vast majority of main roads undergoing 'Macadamisation' by the end of the 19th century. 

McAdam was paid £5,000 for his work with the Bristol Turnpike Trust and was also made Surveyor-General of Metropolitan Roads in 1820. However, his inspired work on road building also made him many enemies.

His new process and management of road works had exposed the corruption and abuse of existing road tolls at the time. Turnpike Trusts were revealed to the public as corrupt in nature, with many running at a deliberate loss despite high toll takings. 

This would cost him financially. His £5,000 (worth about €600,000 today) grant for expenses to the British government was reduced to 'just' £2,000 in 1827. 

What is the 'Macadamisation' process of road building?

McAdam's method for road building vastly simplified the process, as well as improving the longevity of the completed infrastructure. He discovered that massive foundations of rock-on-rock were completely unnecessary. 

Illustration of the construction of a "macadam road", called the "Boonsborough Turnpike Road" between Hagerstown and Boonsboro, Maryland, 1823. Source: FHWA/Wikimedia

He asserted that native soil alone should be enough to support the weight of the road and traffic so long as it was covered by a 'road crust' to prevent erosion of the underlying material. 

Macadam roads were laid as level as possible, with a shallow camber across the structure. For example, on a 9.1m-wide road, the surface would only need to be 7.6cm thick from the edges of the centerline. The road structure was also elevated above the water table. This allowed for rainwater to run off into ditches on either side of the carriageway.

The size of stones was a critical element of McAdam's new roads. The lower 20cm of the road thickness was restricted to stones no larger than 7.5cm in diameter. The upper 5cm layer of stones was about 2cm in diameter. Each layer of stone was thoroughly checked for size by workers and supervisors before being laid.

McAdam's designs dictated that no materials that could absorb water and damage the structure through freeze-thaw should be incorporated into the road. He was also determined that nothing should be laid on top of the road surface to 'bind' them. The action of the road traffic would cause the broken stone to merge into a level, solid surface that would withstand weather and traffic.

McAdam's experience with road building had taught him that a layer of broken angular stones would act as a solid mass in their own right. This negated the need for a large stone layer as previously used on roads. As the surface stones were also pretty small, at least smaller than commonly used tyres at the time, they would provide a great running surface for traffic.

Did McAdam or Trésaguet build the first modern road?

As revolutionary as McAdam's road's were, it is important to note that there were some other innovations made to road-building previously. Pierre-Marie-Jérôme Trésaguet, for example, is considered to be one of the first people to systematically improve road building since Roman times. Trésaguet was a French engineer. 

He worked on paving roads in Paris between 1757 and 1764. Trésaguet also worked as the chief engineer for roads in Limoges, where he had the opportunity to find better and cheaper road-building techniques. 

He proposed a new method of building roads consisting of three layers of stones laid on a crowned subgrade with side ditches for drainage. The first two layers consisted of angular, hand-broken, aggregate of 7.6cm diameter to a depth of about 20cm. The third layer was to consist of a roughly 2.5cm aggregate size of around 5cm thick.

This top layer was meant to provide a smoother shape and carriages while protecting the larger stones underneath from iron wheels and horseshoes. Drainage problems were alleviated by adding camber to the road and digging deep ditches on either side of the carriageway.

As the entire structure was laid within a trench, this solution would be plagued with drainage problems.

Which came first, McAdam's or Thomas Telford's modern road?

Thomas Telford was a Scottish engineer and surveyor who took Tresaguet's road-building method and improved upon it. However, he put more emphasis on high-quality stone. For example, Telford noted that some of the problems the French were seeing with their roads could be avoided by using cubical stone blocks.

A well-preserved section of Telford's road. Source: roads.org.uk

He used partially shaped paving stones, called pitchers, with a slightly flat face on the bottom instead of more amorphous hand broken aggregate, like in Tresaguet's method. Telford kept the natural formation level and used masons to camber the road surface on the upper surface of the blocks. 

His solution was to place a 15cm thick layer of stones no bigger than 6cm in diameter on top of the rock foundation, while the bottom layer was made up of large stones 100 mm wide and 75 to 180 mm in depth. The road surface was finished using a mixture of gravel and broken stone. This came to be known as 'Telford pitching'. His roads depended on a resistant structure to prevent water from pooling and weakening the pavement. The carriageway was also above ground level whenever possible.

Where this was not possible, Telford's technique required the area around the road to be drained. Previously to Telford, road builders, especially in Britain, had often ignored the need for drainage. Telford's 'rediscovery' of this principle was a major breakthrough at the time which, paved the way for McAdam's great achievements.

What made macadam roads so effective?

Although Tresaguet's designs had made some headway, as we have previously seen, they had significant issues with drainage. This had been partially improved with Telford's work, but McAdam made drainage the primary consideration for his designs. To achieve this, McAdam required his pavements to be elevated above the surrounding ground – primarily above the water table. 

Telford's roads were also pretty labour-intensive to build and, importantly, to maintain. They required highly skilled masons to be employed to work the foundation stone to provide the road camber. McAdam's solution provided a method by which the road surface would be compacted by traffic over time, a process that was faster to construct and more than adequate for the time. McAdam also put a strong emphasis on continuous maintenance, where required.

Although McAdam had drawn on the failures and success of his predecessors, his complete reliance on broken aggregate rather than shaped stone blocks for structural strength was the biggest paradigm shift in road construction. His success was also due to his efficient administration and his strong view that road managers needed skill and motivation.

Was 'Tarmac' invented by John McAdam?

In short, no. 

Long after McAdam's death in 1836, the advent of the motor car caused serious problems for the now very popular Macadam roads. As fast-moving cars moved over the road surface, they would create an area of low pressure. This would suck dust from the surface, creating large dust clouds and damaging the road integrity. 

Source: SeppVei/Wikimedia

In 1901 a Swiss doctor, Ernest Guglielminetti, noted that the surface could be coated with tar to solve this problem. He came upon the idea of using tar from Monaco's Gasworks for binding the dust.

A little later, a mixture of coal tar and ironworks slag was patented by Edgar Purnell Hooley as 'tarmac'.

The improved durability that this surfacing provided has meant that most stretches of Macadam roads have been resurfaced since the 1920s. So ubiquitous were Macadam roads across the world, especially in the US, that even modern roads are sometimes referred to as Macadam despite actually being constructed of asphalt or concrete. 

This also applies to 'Tarmac' which is often still colloquially used to describe asphalt roads or runways. 

Death and legacy 

John Loudon McAdam died on November 26, 1836, in Moffat, Dumfriesshire, Scotland. He was returning to his home in Hoddesdon, Hertfordshire, at the time, after enjoying a summer visit to Scotland.

John McAdam's gravestone in Moffat Cemetry. Source: Hugh Trainer/Flickr

His three sons and four grandsons would follow in their venerable ancestor's footsteps and assist future governments in managing turnpike trusts across the UK. His second surviving son, James Nicoll McAdam, the 'Colossus of Roads', was knighted for managing turnpike trusts: a knighthood. It is said that the title was previously offered to his father but declined. 

John Loudon McAdam's contribution to engineering, more specifically road building, changed the world forever. Although this process has been refined over time, the basic principle is still in use today.