Macadamised is not nuts
First of all, Happy Birthday to Jane Austen! One of my favorite authors of all time, and my favorite Regency author—of course! How much we are indebted to her for the whole Regency romance thing!
In an earlier post, I rhapsodized about sidewalks, and now I’m going to do it again—but about roads.
Time was, roads were made up of rocks held together by mud, and you can see by the above picture how effective that construction was against wet weather. The mud would thicken and heave up the rock, or turn into a quagmire, or it would run off altogether, leaving bare chunks of stone that were next to impossible to get your vehicle—let alone the horses—over.
Enter John Louden McAdam, a Scottish engineer who made his fortune in a counting house before turning his attention to the state of the roads. He began in Scotland with the Ayreshire Turnpike Trust, where he learned just how ineffective the prevailing road construction and repair methods were. Then he moved to Bristol, England, where he was appointed as General Surveyor to the Bristol Corporation in 1804.
After experimenting on roads around Bristol and Bath, with positive results, he presented treatises to Parliament beginning in 1816, convincing government to approve drastic changes to road construction practices, including in materials used, and initiated a huge reconstruction project that would revolutionize the roadways of the British Isles, and then beyond.
What is a Macadamised road? Well, it is carefully constructed with layers of of rock and gravel, with a slight curvature, so that rainwater would run off quickly and not soak into the road and ruin the foundation. The rock layer was made up of stones no larger than 7.5 cm (3 in), which was covered by a 5 cm (2 in) layer of gravel no larger than 2 cm (.75 in) each. This top layer was not pressed down during construction—rather, the regular traffic of the road compressed it into a tight, solid mass that was weatherproof enough to last for decades.
John McAdam’s process was so much simpler and less labor intensive than previous methods that it quickly caught on and spread through the British Isles, and then to the US and beyond. His process was improved upon by later engineers, who added different types of binders, including tar—hence the birth of the word “tarmac.”
So the next time your city does a major road reconstruction, think of people like the poor driver of the vehicle pictured above, and thank John McAdam that you live after his time.
