Editing Macadam (section)

===Thomas Telford===
[[File:Laying Telford, Aspinwall, Pennsylvania, 1908.jpg|thumb|Laying Telford paving in [[Aspinwall, Pennsylvania]], in 1908]]
[[Thomas Telford]], born in [[Dumfriesshire]], [[Scotland]],<ref>{{cite book |title=The Life of Thomas Telford, Civil Engineer |last=Smiles |first=Samuel |author-link=Samuel Smiles |year=1867 |publisher=John Murray |location=London |pages=[https://archive.org/details/lifethomastelfo01smilgoog/page/n373 331] |url=https://archive.org/details/lifethomastelfo01smilgoog |access-date=27 September 2011}}</ref> was a surveyor and engineer who applied Tresaguet's road building theories. In 1801 Telford worked for the [[Commissioners of Highland Roads and Bridges|Commission of Highland Roads and Bridges]]. He became director of the [[Holyhead]] Road Commission between 1815 and 1830. Telford extended Tresaguet's theories but emphasized high-quality stone. He recognized that some of the road problems of the French could be avoided by using cubical stone blocks.<ref name=Lay1992p74>Lay (1992), p.74</ref>

Telford used roughly {{convert|12|x|10|x|6|in|cm|abbr=on}} partially shaped paving stones (pitchers), with a slight flat face on the bottom surface. He turned the other faces more vertically than Tresaguet's method. The longest edge was arranged crossways to the traffic direction, and the joints were broken in the method of conventional [[brickwork]] but with the smallest faces of the pitcher forming the upper and lower surfaces.<ref name=Lay1992p74/>

Broken stone was wedged into the spaces between the tapered perpendicular faces to provide the layer with good lateral control. Telford kept the natural formation level and used masons to camber the upper surface of the blocks. He placed a {{convert|6|in|cm|adj=on}} layer of stone no bigger than {{convert|6|cm|in|abbr=on|order=flip}} on top of the rock foundation. To finish the road surface he covered the stones with a mixture of [[gravel]] and broken stone. This structure came to be known as "Telford pitching." Telford's road depended on a resistant structure to prevent water from collecting and corroding the strength of the pavement. Telford raised the pavement structure above ground level whenever possible.{{Citation needed|date=April 2021}}

Where the structure could not be raised, Telford drained the area surrounding the roadside. Previous road builders in Britain ignored drainage problems, and Telford's rediscovery of drainage principles was a major contribution to road construction.<ref name="Lay1992p75">Lay (1992), p.75</ref> Notably, around the same time, [[John Metcalf (civil engineer)|John Metcalf]] strongly advocated that drainage was in fact an important factor in road construction and astonished colleagues by building dry roads even through marshland. He accomplished this by incorporating a layer of brushwood and heather.{{Citation needed|date=April 2021}}