- published: 17 Sep 2015
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A stack interchange (also known as a spaghetti road or a butterfly junction from its bird's-eye profile) is a free-flowing grade separated junction between two roads.
In countries where one drives on the right, left turns are handled by semi-directional flyover/under ramps. Vehicles first exit the main carriageway to the right, then complete the turn via a ramp which crosses both highways, eventually merging with the traffic turning right from the opposite side of the interchange. A stack interchange, then, has two pairs of left-turning ramps, which can be "stacked" in various configurations above or below the two interchanging highways.
In countries where one drives on the left, the appearance of the junction is topologically identical, but traffic flows are reversed.
Stacks eliminate the problems of weaving and have the highest vehicle capacity among different types of four-way interchanges. However, they require considerable and expensive construction work for their flyover ramps. Stack interchanges are also widely considered to be an eyesore among residents of homes near existing or proposed interchanges, leading to considerable NIMBY opposition.
Samuel "Sam" Houston (March 2, 1793–July 26, 1863), was a nineteenth-century American statesman, politician, and soldier. He was born in Timber Ridge in the Shenandoah Valley of Virginia, of Scots-Irish descent. Houston became a key figure in the history of Texas and was elected as the first and third President of the Republic of Texas, U.S. Senator for Texas after it joined the United States, and finally as a governor of the state. He refused to swear loyalty to the Confederacy when Texas seceded from the Union in 1861 with the outbreak of the American Civil War, and was removed from office. To avoid bloodshed, he refused an offer of a Union army to put down the Confederate rebellion. Instead, he retired to Huntsville, Texas, where he died before the end of the Civil War.
His earlier life included migration to Tennessee from Virginia, time spent with the Cherokee Nation (into which he later was adopted as a citizen and took a wife), military service in the War of 1812, and successful participation in Tennessee politics. Houston is the only person in U.S. history to have been the governor of two different states (although other men had served as governors of more than one American territory).