• Source: List of auxiliary Interstate Highways

Auxiliary Interstate Highways (also called three-digit Interstate Highways) are a subset of highways within the United States' Interstate Highway System. The 323 auxiliary routes generally fall into three types: spur routes, which connect to or intersect the parent route at one end; bypasses, which connect to the parent route at both ends; and beltways, which form a circle that intersects the parent route at two locations. Some routes connect to the parent route at one end but to another route at the other end; some states treat these as spurs while others treat them as bypasses. Like the primary Interstate Highways, auxiliary highways meet Interstate Highway standards (with rare exceptions).
The shorter auxiliary routes branch from primary routes; their numbers are based on the parent route's number. All of the supplement routes for Interstate 95 (I-95) are designated with a three-digit number ending in "95": I-x95. With some exceptions, spur routes are numbered with an odd hundreds digit (such as I-395), while bypasses and beltways are numbered with an even hundreds digit (such as I-695). Because longer Interstates may have many such supplemental routes, the numbers can repeat from state to state along their route, but they will not repeat within a state.
There are three states that have no auxiliary Interstate Highways: Alaska, Arizona, and New Mexico. North Dakota has an auxiliary route, but it is unsigned, and Wyoming's does not meet Interstate Highway standards.




Terminology and guidelines



Auxiliary Interstates are divided into three types: spur, loop, and bypass routes.
The first digit of the three digits usually signifies whether a route is a bypass, spur, or beltway. The last two digits are derived from the main Interstate Highway. For instance, I-115 contains an odd number in the first digit (1), which indicates that this freeway is a spur. The last two digits signify the highway's origin. In this case, the "15" in I-115 shows that it is a supplement to I-15.
Exceptions to the standard numbering guidelines exist for a number of reasons. In some cases, original routes were changed, extended, or abandoned, leaving discrepancies in the system. In other cases, it may not be possible to use the proper number because the limited set of available numbers has been exhausted, causing a "non-standard" number to be used.




= Spur route

=
A spur route's number usually has an odd number for its first digit. It is usually one of the following:

It may serve another section of a city or metropolitan area not served by the main freeway (most often the central business district), terminating at a regular city street/avenue or at a substandard freeway, such as I-185 in Columbus, Georgia.
It may represent the first portion of a contemplated extended freeway that does not currently meet Interstate Standards but it may be upgraded later on. An example is I-369 in Texas, which currently does not connect with parent route I-69.
It may connect two unrelated Interstate highways, like I-390 in New York State and I-355 in Illinois.
States differ on their interpretation of the numbering convention when an Interstate behaves in this case In the I-390 example above, the route is assigned odd first digit. The I-275 in Tennessee, a connector between I-40 and I-75, is assigned an even first digit.
This may even vary within the same state. For example, in Michigan, both I-196 and I-696 intersect I-96 at one end and I-94 at the other end.
Examples include:

I-110 in California links I-10 with the Port of Los Angeles. This freeway was built before the creation of the Interstate Highway System as the Harbor Freeway, and was later adopted into the Interstate Highway System.
I-180 in North-Central Pennsylvania connects Williamsport and Lycoming County with I-80 in Milton, but does not actually enter Lycoming County. I-180 also serves as a connection to those traveling to New York and I-86 via U.S. Route 15 and the Future I-99 Corridor at its western terminus.
I-190 in New York connects the cities of Niagara Falls and Buffalo with I-90.
Sometimes, a three-digit Interstate Highway branches off from another three-digit Interstate Highway. These spurs do not connect directly with their parent highways, but are associated with them via the three-digit highways they do intersect with.
Examples include:

I-380, located in the San Francisco Bay Area of Northern California begins at I-280 and connects with US 101 at San Francisco International Airport.
I-190 in Massachusetts branches off from I-290 near Worcester.
I-795 in Baltimore County, Maryland branches off from I-695.




= Bypass

=
A bypass route may traverse around a city, or may run through it with the mainline bypassing. In a typical 3-digit Interstate Highway, bypasses usually have both its two termini junctioned with another Interstate highway. Bypass routes are preceded by an even number in the first digit.
Examples include:

I-220 in Louisiana serves as a bypass of downtown Shreveport.
I-440 forms a loop around the south side of Nashville.
I-890 travels through downtown Schenectady, which I-90 avoids.
In the case of an auxiliary Interstate highway which has both ends at Interstates but not the same Interstate, some states treat these as bypasses while others treat these as spurs—see Spur route above.




= Beltway

=
A beltway (also known as a loop route) completely surrounds a metropolitan city, and it is often connected with multiple junctions to other routes. Unlike other auxiliary Interstate Highways (and by extension, all primary Interstate Highways), beltways do not have termini; however, they have a place where the highway mileage resets to zero. Beltways are also preceded by an even number in the first digit.
Some examples of beltways include:

I-275 in Ohio, Kentucky and Indiana encircles the city of Cincinnati.
I-465 in Indiana encircles the city of Indianapolis.
I-495 in Maryland and Virginia encircles the city of Washington, D.C., and is referred to as "The Capital Beltway".




Auxiliary Interstates


Note: this table sorts the route numbers by parent highway.




See also


U.S. Roads portal




Notes






References






External links


Geographic data related to List of auxiliary Interstate Highways at OpenStreetMap
3-digit Interstates at Kurumi.com

Kata Kunci Pencarian:

• Interstate 485
• Interstate 15 di Nevada
• Interstate 185 (Georgia)
• Interstate 35
• Interstate 805
• List of auxiliary Interstate Highways
• List of Interstate Highways
• List of future Interstate Highways
• Interstate 184
• Interstate 225
• Interstate 115
• Interstate 585
• Interstate 505
• Interstate 238 and State Route 238 (California)
• Interstate 535