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In the field of road transport, a turnaround is a type of junction that allows traffic traveling in one direction on a road to efficiently make a U-turn (to reverse course and travel the opposite direction) typically without backing up or making dangerous maneuvers in the middle of the traffic stream. While many junction types permit U-turns, the term turnaround often applies to road junctions built specifically for this purpose. ==Junction types designed specifically for U-turns== The following road junction types are designed specifically to allow U-turns. * The Texas U-turn allows traffic traveling on one direction of a one-way frontage road, running parallel to a highway, to cross the highway (via a grade separation) and turn onto the other frontage road, traveling in the opposite direction. The term refers to roadworks which are specially built for this purpose; and does not refer to use of an intersecting roadway to navigate between frontage roads.〔 〕 * The median U-turn crossover (often called a "Michigan left" in the United States) allows traffic traveling in one direction on a divided highway (typically one with traffic lights and at-grade intersections) to perform a U-turn through the median. * A junction resembling a "backward jughandle" is sometimes found, allowing U-turns. According to the U.S. Federal Highway Administration, this is actually just a variant of a standard median U-turn crossover, built to accommodate roads with medians too narrow to otherwise permit a U-turn to be made safely.〔 〕 Traffic wishing to turn around executes a turn across oncoming traffic (left in countries where traffic drives on the right; right in countries where traffic drives on the left) onto the at-grade ramp (sometimes called a "bulb out" or a "loon"),〔 〕〔 〕 but rather than merging onto a crossing road, the "bulb out" turns back and merges onto the road the traffic just left, in the opposite direction. * *Examples of this can be found on a divided section of U.S. Route 101 in Lincoln Beach, Oregon.〔 〕〔 〕〔 〕〔 〕 * A grade-separated ramp can be used to allow traffic to turn around. * *An example on a controlled-access highway is the Sabine River Turnaround, exit 1 on westbound Interstate 10 in Calcasieu Parish, Louisiana, United States, just before the Sabine River and the Texas border.〔 〕〔 〕 U-turn traffic exits normally onto the U-turn ramp, which forms an underpass below the highway; traffic then rejoins the highway at an eastbound entrance ramp. * *Examples on a controlled-access highway with frontage roads are on the Manuel Gómez Morín Beltway, just north and south of Mariano Otero Avenue in Zapopan, Mexico, just outside Guadalajara.〔 〕〔 〕〔 〕〔 〕 Here, traffic travels to a frontage road, whose inner (left) lane leads to a U-turn ramp which descends and forms an underpass below the beltway; traffic then ascends and joins the inner (left) lane of the opposing frontage road. * *Other examples on a controlled-access highway are on the Damansara–Puchong (E11) Expressway (also known by its Malaysian acronym, LDP), between exit 1114 (the Puchong Jaya Interchange) and exit 1118 (the Puchong Intan Interchange), in Puchong, Malaysia, near Kuala Lumpur.〔 〕 Traffic drives on the left, and the outer (left) lanes serve as hybrid entrance/exit lanes and frontage roads. In each direction, outer-lane traffic can travel to a U-turn ramp which forms an overpass above the LDP. The U-turn ramps come close to each other, but remain separate; no roadway surface is shared by opposing traffic. * *An example on an undivided highway is on the Sanibel Causeway, connecting Sanibel Island with the mainland in South Fort Myers, Florida, United States.〔 〕〔 〕 Traffic traveling toward the mainland can exit onto a U-turn underpass, then return on the causeway to Sanibel Island. * A cul-de-sac allows a smooth turnaround at the end of a dead end street. 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「Turnaround (road)」の詳細全文を読む スポンサード リンク
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