TIL of Macadam roads. These roads were convex, raised a few inches, and made of layered crushed rock; they were state-of-the-art for the 19th century. The rise of automobiles led to the dust issues that were solved by binding the roads with tar, leading to the invention of tarmac.
en.wikipedia.orgSubmitted by jamescookenotthatone t3_1181yq6 in todayilearned
jamescookenotthatone OP t1_j9etovt wrote
Something I found amusing.
>Size of stones was central to the McAdam's road building theory. The lower 8 in (20 cm) road thickness was restricted to stones no larger than 3 inches (7.5 cm). The upper 2-inch-thick (5 cm) layer of stones was limited to stones 2 centimetres (3⁄4 in) in diameter; these were checked by supervisors who carried scales. A workman could check the stone size himself by seeing if the stone would fit into his mouth. The importance of the 2 cm stone size was that the stones needed to be much smaller than the 4 inches (10 cm) width of the iron carriage wheels that travelled on the road.[5]