Terminology
Aunque el nombre parece implicar que las autopistas interestatales tienen recorrido por más de un Estado, muchas no lo hacen. Hay Autopistas Interestatales en Hawái, financiadas de la misma forma que en otros Estados, pero que discurre en su totalidad en la populosa isla de Oahu. Tienen la denominación de "H-X" y conectan bases militares. De manera análoga, Alaska y Puerto Rico tienen carreteras que reciben financiación del programa de autopistas interestatales, aunque dichas rutas no han sido señalizadas como tales, solo sobre el papel.
Primary routes
Interstate highways are commonly referred to as Interstate XX or I-XX, where "XX" is the two-digit number of the route; Interstate Highway XX (IH XX) or Interstate Route XX (IR XX) is sometimes used. In some areas, the more generic Route XX or Highway XX is also used.
The nomenclature of the interstate highway network (as well as the United States highway network) is managed by the American Association of State Highway and Transportation Administrations (AASHTO), although its authority is occasionally undermined by designations imposed by federal law. Within the continental United States, primary interstate highways (also called priority routes or two-digit interstate highways) are defined by one- or two-digit numbers. Most interstates are double digits; There are only three single-digit Interstates on the network: Interstate 4, I-5, and I-8. Within this category, those with an east-west orientation have even numbering and those with a north-south orientation have an odd number. The odd numbering increases from west to east and the even numbering from south to north. An exception to this rule is I-75 which is east of I-85" south of Atlanta. This is not the case north of Atlanta. Numbering that is divisible by 5 is considered among the primary interstates, supporting long-distance traffic. For example, I-5 runs from Canada to Mexico along the west coast (the only Interstate that does so) while I-95 runs between Miami and Canada. Additionally, I-10 (en) runs from Santa Monica, California to Jacksonville, Florida while I-90 runs from Seattle to Boston. However, not all primary interstates whose numbering is divisible by 5 are long-haul. I-45 runs from Galveston "Galveston (Texas)") to north of Dallas, with a length of only 284 miles. It is the only primary interstate with numbering divisible by 5 that does not cross interstate borders. See List of Interstates whose route runs through only one State") for other primary interstates that do not cross interstate borders.
It should be noted that there are no interstates I-50 and I-60 (and that there are no even-numbered interstates between 46 and 62), mainly because in the same States they should pass through there are already US 50 "U.S. Route 50 (Nevada)") and US 60 "U.S. Route 60 (Arizona)"). AASHTO is required to prevent Interstates and US Highways from having the same numbering within the same State, although I-24") and US 24") have their terminus in Illinois. Some interstates do not follow this rule — I-69") will overlap US 69") in Lufkin "Lufkin (Texas)"),[6] I-74") will overlap US 74 ("") in North Carolina, and I-41") will overlap US 41") in Wisconsin.
Several highways with two-digit numbering are made up of two separate sections without continuity, namely I-76"), I-84"), I-86") and I-8"). Some of these highways are the result of the change in the numbering system in the 70s; Previously, a letter was used as a suffix for branches of primary routes; For example, the western portion of I-84") was I-80N, as if coming from the north from I-80. In the 1970s, AASHTO decided to eliminate these suffixes; some of these sections became other two-digit highways, while others became three-digit highways (see below). Only two pairs of suffix-numbered highways exist; I-35 was split into I-35W") and I-35E") in the Dallas-Fort Worth and Minneapolis-St Paul areas, respectively.
For the sake of greater efficiency, some interstates have concurrent routes on short stretches, although sometimes they do so over long distances. These are called "concurrent stretches." An example of this is where I-75") and I-85") converge in the Atlanta metropolitan area to form the Downtown Connector"), the main thoroughfare through the city. Another example is the convergence and divergence of interstates I-90 and I-94, which occur several times as they travel through the northern Midwest and the Great Plains. I-90 and I-94 to the junction with I-39 from Madison, WI") to Portage, WI"), creating the longest stretch of concurrency of three Interstates in the Network. A new example is the I-73/I-74x convergence, which runs along the U.S. Highway. Route 220") from Asheboro&action=edit&redlink=1 "WAsheboro (North Carolina) (not yet drafted)") to Rockingham "Rockingham (North Carolina)"). I-73 also shares a route with I-40 and I-85 in the Greensboro Urban Loop"), a new bypass to Greensboro (North Carolina) "Greensboro (North Carolina)"). Strict compliance with Internet addresses causes amusing dysfunctions. During a 9-mile stretch east of Wytheville&action=edit&redlink=1 "Wytheville (Virginia) (not yet redacted)"), the driver may be traveling on both I-81 North and I-77 South (and vice versa).
Three-digit interstates
Auxiliary interstate highways have three digits in their numbering, which is formed by a number in front of the two digits of the primary interstate highway, to designate branches or loops that branch off from any primary route or its auxiliary sections. A branch is a highway that deviates from the main highway and does not end at another Interstate, it has an odd number in its first digit. A loop is a highway that returns to the main highway, it has an even number in its first digit. The number given to the first digit of a route branching from its main route to the end of another Interstate depends on the State; some consider these routes as branches and assign them odd numbers, while others consider them connecting loops by giving them even numbers.
Where primary two-digit interstate highways have letters as suffixes, their auxiliary interstates are numbered without the letter.
Due to the large number of these auxiliary interstates (also known as spur routes) the numbering may be repeated in the various States through which the primary interstate runs; However, there are no two three-digit Interstates with the same numbering in the same state. For example, I-90(en)&action=edit&redlink=1 "I-90(en) (not yet redacted)") in New York has the entire collection of three-digit interstates possible - I-190"), I-290"), I-390"), I-490"), I-590"), I-690"), I-790"), I-890"), I-990").
The ring roads to large cities usually retain the name throughout the route, even when they run through other States. For example, Cincinnati, like many other cities, has a large beltway surrounding it that crosses the early interstate highways I-71"), I-74"), and I-75") and runs through Ohio, Kentucky, and Indiana. The entire 84 miles are signed as I-275"). (It is also the only auxiliary Interstate that runs through three states).
Also, the beltway around Washington D.C., known as the Capital Beltway, simultaneously supports interstates I-95 and I-495. Originally, the beltway was only I-495, as I-95 was planned to run through Washington, but in 1977 said interstate was rerouted through the western half of said beltway due to the cancellation of the section that was going to connect the center of the city with College Park, Maryland, while I-495 remained in the western half. I-495 was later added to the eastern half of the beltway in 1989, creating a rare case of concurrency on the same route of a primary interstate with one of its auxiliaries. Another example of this type of concurrency is I-40") and I-440") in Raleigh (North Carolina), North Carolina.
Exceptions
I-238, near Oakland (California), is one of the two major exceptions to interstate highway numbering, as there is no I-38. This number exists because I-238 replaced a stretch of State Route 238" and there was no available number derived from its Primary Interstate, I-80. The other exception is I-99 in Pennsylvania, the origin of which is a law passed by Pennsylvania Congressman Bud Shustern"); I-99 (also called U.S. Route 220) is west of several Interstate Highways numbered less than 99, but 99 was the closest two-digit odd numbering available for this Interstate.
A less important exception is I-82"), which runs its entire length north of I-84"); This is a remnant of I-84 that previously had the name I-80N.
Some proposed new Interstate Highways have continued to have similar non-compliant names because of the politicians who introduced them. For example, sponsors of the proposed Third Infantry Division Highway, a highway in Georgia and Tennessee, have suggested that it be named Interstate 3, in honor of the 3rd Infantry Division.
The following two-digit Interstate Highways have changed their established direction (even=east-west, odd=north-south):.
• - I-69") east of Lansing, Michigan.
• - I-76") in Nebraska.
The I-69 segment is an extension of its original route; I-76 only runs for two miles in Nebraska before ending at I-80.
The Interstate Highways in Hawaii, as well as the "virtual" ones in Alaska and Puerto Rico, are numbered according to the order of construction, without following the rules of odd and even numbering.
The naming of the Interstate Business Loop and Business Spur is not subject to any of the Interstate Highway Network identification standards. Its designation is simple: a Business Spur leads to a downtown area by starting from and returning to its Primary Interstate, while a Business Spur ends in the center of the city or, in some cases, continues from the end of a Primary Interstate. Business routes can be divided into Interstates, either two or three digits, and can be repeated within a state. In some cases, when an Interstate has been realigned, the old road has been designated as a Business Loop, since it cannot follow established regulations.