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The Historic Pacific Highway
in Washington

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Macadam Road



In 1912 the first Macadam-paved road in Washington State was in Tukwila and bears the name of this new method of street paving.

This road was used as one of 2 routes from Seattle to Tukwila in the early to late teens to about 1920.

Macadam consists basically of compacted layers of small stones cemented into a hard surface by means of stone dust and water (water-bound macadam). However, the main pavement surfaces in use today are bituminous/asphalt coverings and concrete.

The macadam method of road building uses a layer of well drained and compacted subsoil to support the load weight of the roadway, while the top layer acts as a wearing surface built only to shed water. Modern day macadam road construction is based on this practice and is used worldwide.

The top layer of a macadam road is mostly made of asphalt and rocks, now some builders use other ingredients to help deter road wear and add traction to the surface. 

Nowadays asphalt is made synthetically, but true asphalt in its natural state was originally found in only one place in the world, in a pitch lake on Trinidad Island.

 


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