19/9/13

The Dwight D. Eisenhower National System of Interstate and Defense Highways (commonly known as the Interstate Highway System, Interstate Freeway System, Interstate System, or simply the Interstate) is a network of freeways that forms a part of the National Highway System of the United States. The system is named for President Dwight D. Eisenhower, who championed its formation. Construction was authorized by the Federal Aid Highway Act of 1956, and the original portion was completed 35 years later. The network has since been extended, and as of 2010, it had a total length of 47,182 miles (75,932 km),[2] making it the world's second longest after China's. As of 2010, about one-quarter of all vehicle miles driven in the country use the Interstate system.[3] The cost of construction has been estimated at $425 billion (in 2006 dollars).[4]

Although the system was proclaimed complete in 1992, two of the original interstates, I-95 and I-70, are not contiguous because they are missing interchanges. Both of these discontinuities are due to local opposition, which has blocked efforts to build the necessary connections to fully complete the system.
Because of the cancellation of the Somerset Freeway, I-95 is discontinuous in New Jersey. Authorized by the federal government in 2004, the Pennsylvania Turnpike/Interstate 95 Interchange Project is scheduled to connect the separate sections of I‑95 to form a continuous route, completing the final section of the original plan. Construction began in 2010.[22]
There is a missing interchange between the Pennsylvania Turnpike and I-70 near Breezewood, Pennsylvania, where traffic must use a few blocks of US 30, which are cluttered with services, to rejoin I-70. Although solutions have been proposed through the years to complete the discontinuity on I-70, they have been blocked by local opposition.
Additional spurs, loops, and bypasses remain under construction, such as I-485 in North Carolina, which has been under construction since the 1980s. A few main routes not part of the original plan remain under construction, such as I-22 in Tennessee, Mississippi and Alabama, and the extension of I-69 from Indiana to Texas. Officials have also identified some non-Interstate corridors for future inclusion into the system, either by construction of new Interstate routes or upgrade of existing highways and roads to meet Interstate standards.
I-49, formerly within Louisiana, was designated as an expansion corridor, and FHWA approved the expanded route north from Lafayette, Louisiana, to Kansas City, Missouri. The new I-49 northern expansion into Arkansas and Missouri is under construction with various new freeway sections already designated with the I-49 number. In late 2012, the northernmost section (formerly US 71) was officially designated I-49 from the I-470 junction south of Kansas City, Missouri, to the I-44 junction at Joplin, Missouri.[23]