Английский язык в транспортно-логистической системе

covered by a road crust that would protect the soil under-neath from water and wear. Macadam roads were adequate for use by horses and carriages or coaches, but they were very dusty and subject to erosion with heavy rain. Methods to stabilize macadam roads with tar date back to at least 1834 when John Henry Cassell, operating from Cas-sell's Patent Lava Stone Works in Milwall, patented «Pitch Macadam». This method involved spreading tar on the sub-grade, placing a typical macadam layer, and finally sealing the macadam with a mixture of tar and sand. Tar-grouted mac-adam was in use well before 1900, and involved scarifying the surface of an existing macadam pavement, spreading tar, and re-compacting. Although the use of tar in road construction was known in the 19th century, it was little used and was not introduced on a large scale until the motorcar arrived on the scene in the early 20th century. Modern tarmac was patented by British civil engineer Edgar Purnell Hooley, who noticed that spilled tar on the roadway kept the tar down and created a smooth surface. Today, roadways are primarily asphalt or concrete. Both are based on McAdam's concept of stone aggregate in a bind-er, asphalt cement or Portland cement respectively. Asphalt is known as a flexible pavement, one which slowly will "flow" un-der the pounding of traffic. Concrete is a rigid pavement, which can take heavier loads but is more expensive and requires more carefully prepared subbase. So, generally, major roads are con-crete and local roads are asphalt. Concrete roads are often covered with a thin layer of asphalt to create a wearing sur-face. Modern pavements are designed for heavier vehicle loads and faster speeds, requiring thicker slabs and deeper subbase. Subbase is the layer or successive layers of stone, gravel and sand supporting the pavement. It is needed to spread out the slab load bearing on the underlying soil and to conduct aw...