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There's a joke in Houston regarding evacuation routes in case of a hurricane. Louisianans use I-10 east. Cowboy fans use I-45 north. And Aggies fans use Loop 610.
4.52 miles ; a loop of I-10 (actually, I-610 goes straight and I-10 does the looping) plows through New Orleans.
The idea for I-610 dates back to about 1956, when a consulting firm proposed building a federal-aid highway in that location. The corridor cut across City Park, alongside a nearby railway. Public hearings were held in 1958, and the park location was subject to considerable debate. In October 1962, a six-lane design was approved. 
In 1966, the state purchased right-of-way through the park. Construction began in 1971. The following year, a lawsuit was brought against the highway, citing a 1968 law forbidding use of parkland for expressways unless there is no feasible alternative and all possible plans are made to minimize parkland damage. 
Sometime since then, construction resumed and I-610 was completed.
37.97 miles ; full beltway around Houston. Also known as "Loop 610", Interstate 610 is one of less than a dozen true 3di loops. Completed in 1973.
The idea for a loop around Houston dates back to the 1930s, when city planners proposed a ring road to relieve downtown traffic. The northern section was the first to have its alignment approved, in 1941.
Construction began on the North Loop in the 1950s, and when Interstate system mileage was apportioned, Houston's loop was approved -- in part. On Oct. 1, 1959, the Bureau of Public Roads (BPR) approved I-610 at a location leading from I-10 east of Houston looping north, west, south, and east to end at I-45 southeast of Houston -- a "C" shape. 
In 1962, Texas lobbied for inclusion of the East Loop and its bridge towering over the Houston Ship Channel. On Sept. 6, 1962, BRP approved this.  The bridge opened in 1973, completing Loop 610.