John Loudon McAdam, surveyor to the Bristol turnpike trust, showed from 1816 that a road needs no massive stone foundation if it is raised above the water table and surfaced with graded, angular broken stone that keys together under traffic and sheds water through a camber. Cheap and quickly laid, macadam replaced setts and gravel on turnpikes and city streets; tar-bound versions (tarmacadam) followed once motor traffic began stripping the dust binder. In parallel, natural bitumen sheet asphalt was laid in Paris from the 1850s, and Edward de Smedt's sheet asphalt at Newark in 1870 and on Pennsylvania Avenue in Washington from 1877 gave a smooth, washable, near-silent surface. Kerbs, gutters, gullies and the modern cross-section came with it.
Paving is the least visible and most consequential street technology: it fixed the carriageway-footway division, made the road a drainage device, and cut noise, mud and dust enough to change what streets could be used for. Smooth surfaces enabled the bicycle, then the fast motor vehicle, and the cheapness of asphalt underwrote 20th-century road building and suburban subdivision at continental scale. It also produced the impervious city surface now driving flood and heat-island retrofits.
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