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A dual carriageway (North American English: divided highway) is a class of highway with dual carriageways for traffic travelling in opposite directions separated by a central reservation (North American English: median). Roads with two or more carriageways which are designed to higher standards with controlled access are generally classed as motorways, freeways, etc., rather than dual carriageways. A road without a central reservation is a single carriageway (North American English: undivided highway) regardless of the number of lanes. Dual carriageways have improved road traffic safety over single carriageways and typically have higher speed limits as a result. In some places, express lanes and local/collector lanes are used within a local-express-lane system to provide more capacity and to smooth traffic flows for longer-distance travel. ==History== A very early (perhaps the first) example of a dual carriageway was the ''Via Portuensis'', built in the first century by the Roman emperor Claudius between Rome and its port Ostia at the mouth of the Tiber. In 1907 the Long Island Motor Parkway opened, and roughly 20% of it featured a semi-dual-carriageway design. The New York City Belt Parkway system, which was built between 1907 and 1934, also pioneered the same design. However the majority of it featured concrete or brick railings as lane dividers instead of grass medians. In 1924 the first Italian ''autostrada'' was opened running from Milan to Varese. It featured a broad road bed and did not feature lane dividers except near cities and through the mountains.〔(【引用サイトリンク】 title=German Myth 8: Hitler's Autobahn? )〕〔(【引用サイトリンク】 title=1924 Mile Posts )〕 The London end of the Great West Road became Britain's first dual carriageway when it was opened in 1925 by King George V. In 1927 the Rome bypass was opened. It ran bypassing Rome to the east. Almost the entire length featured a dual-carriageway design. In the early 1930s it was extended southward all the way to Naples and northward to Florence. Most of the original routing was destroyed by the Allies in the World War II. By 1930 several US and European cities had built dual-carriageway highways, mostly to control traffic jams and/or to provide bypass routes for traffic. In 1932 the first German ''autobahn'' opened between Cologne and Bonn. It ran and became a precedent for future highways. Although it, like the first ''autostrada'', did not feature a dual-carriageway design, it inspired the mass construction of future high-speed roadways. During the 1930s, Germany, Italy, and the Soviet Union began construction of a network of dual carriageway expressways. By 1942, Germany had over of dual carriageway roads, Italy had nearly , and the Soviet Union had . What may be the world's first long-distance intercity dual carriageway/freeway is the Queen Elizabeth Way in Southern Ontario in Canada, initially linking the large cities of Toronto and Hamilton together by 1939, with construction on this stretch of the present-day Queen Elizabeth Way beginning in 1936 as "Middle Road". Opened to traffic in 1940, the long Pennsylvania Turnpike was the first rural dual carriageway built in the United States. By 1955 several states had built dual carriageway freeways and turnpikes and in 1957 the Interstate Highway System began. Completed in 1994, the major highway system links all the major cities of the United States. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「dual carriageway」の詳細全文を読む スポンサード リンク
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