Interstate Highway System

[edit] Standards

Main article: Interstate Highway standards

The American Association of State Highway and Transportation Officials (AASHTO) has defined a set of standards that all new Interstates must meet unless a waiver from the Federal Highway Administration (FHWA) is obtained. These standards have become more strict over the years.^{[citation needed]} One almost absolute standard is the controlled access nature of the roads. With few exceptions, traffic lights (and cross traffic in general) are limited to toll booths and ramp meters (metered flow control for lane merging during rush hour).

[edit] Speed limits

Further information: Speed limits in the United States

Interstate highways often have the highest speed limits in a given area. Speed limits are determined by individual states.^{[citation needed]} Rural limits generally range from 65 to 80 mph (100 to 129 km/h) typically with the lower limits in the more populated northeastern states and the higher speeds in the western states^{[citation needed]}, with the exception of Oregon's state speed limit ceiling of 65 mph.^{[citation needed]} Urban Interstate speed limits are generally 50 to 65 mph (80.5 to 104.6 km/h) across the country.^{[citation needed]}

[edit] Dual-purpose design

Further information: Contraflow lane reversal

In addition to being designed to support automobile and heavy truck traffic, Interstate highways are also designed for use in military and civil defense operations, particularly troop movements.^{[citation needed]}

One potential civil defense use of the Interstate Highway System is for the emergency evacuation of cities in the event of a nuclear war.^{[citation needed]} The system has already been used to facilitate evacuations in the face of hurricanes and other natural disasters.

An option for maximizing traffic throughput on a highway is to reverse the flow of traffic on one side of a divider so that all lanes become outbound lanes. This procedure, known as contraflow, was first employed on highway I-16 in the 1999 evacuation of Savannah, Georgia in anticipation of Hurricane Floyd.^{[citation needed]} In 2004, contraflow was employed ahead of Hurricane Charley in the Tampa, Florida area and on the Gulf Coast before the landfall of Hurricane Ivan.^[9] It was again used in 2005 during the evacuations of New Orleans, Louisiana, and Houston, Texas, prior to hurricanes Katrina and Rita, respectively.^{[citation needed]}

A widespread urban legend states that one out of every five or ten miles of the Interstate Highway System must be built straight and flat so as to be usable by aircraft during times of war. Contrary to popular lore, Interstate highways are not designed to serve as airstrips. ^[10][11]

[edit] Terminology

While the name implies that Interstate highways cross state lines, many do not (for details see List of intrastate Interstates). Rather, they are funded federally with money shared among the states. There are Interstate highways in Hawaii, funded in the same way as in the other states, but entirely within the populous island of Oahu. They have the designation of H-<math>x</math> and connect military bases, though they are open to public use. Both Alaska and Puerto Rico have public roads that receive funding from the Interstate program, although these routes are not signed as Interstate highways (except on paper). These roads are neither planned for, nor built to, official Interstate highway standards.

[edit] Primary routes

See also: List of Interstate Highways

Interstate highways are typically known as Interstate XX or I-XX, where "XX" is the one- or two-digit route number; sometimes Interstate Highway XX (IH XX) or Interstate Route XX (IR XX) is used. In some areas, the more generic Route XX or Highway XX is used, or in the case of Southern California and Nevada, The XX.

The numbering scheme for the Interstate Highway System (as well as the U.S. Highway System) was developed in 1957 by the American Association of State Highway and Transportation Officials (AASHTO) and is still coordinated by them, though their authority is occasionally trumped by a number written into federal law. Within the continental United States, primary Interstates (also called main line Interstates or two-digit Interstates) are given one- or two-digit route numbers. Most Interstates have two digits; there are only three one-digit Interstates in the system: I-4, I-5 and I-8.

Within this category, east/west highways are assigned even numbers, and north/south highways are assigned odd numbers. Odd route numbers increase from west to east, and even-numbered routes increase from south to north, though there are exceptions to both principles in several locations. Numbers divisible by 5 are intended to be major arteries among the primary routes, carrying traffic long distances.^{[citation needed]} For example, along the west coast, I-5 runs between Canada and Mexico (the only Interstate to do so) while I-95 runs between Miami and Canada along the east coast. In addition, I-10 runs between Santa Monica, California and Jacksonville, Florida, while I-90 runs between Seattle and Boston. However, not all primary routes divisible by 5 traverse long distances. I-45 runs between Galveston, Texas and Dallas, a distance of only 284 miles (457 km). It is the only primary route divisible by 5 that does not cross state lines. See List of intrastate Interstate Highways for other primary routes that do not cross state lines.

I-50 and I-60 do not exist (and there are no even-numbered Interstates from 46 to 62), mainly because they would most likely have passed through the same states that already have US 50 and US 60. AASHTO rules discourage Interstate and U.S. highways having the same number within the same state, although I-24 and US 24 exist at opposite ends of Illinois. Some planned Interstates do not follow this guideline — I-69 will intersect US 69 in Lufkin, Texas^[12], I-74 will overlap US 74 in North Carolina, and I-41 will do the same with US 41 in Wisconsin.

Several two-digit numbers are shared between two roads at opposite ends of the country, namely I-76, I-84, I-86 and I-88. Some of these were the result of a change in the numbering system in the 1970s; previously letter-suffixed numbers were used for long spurs off primary routes; for example, western I-84 was I-80N, as it went north from I-80. In the 1970s, AASHTO decided to eliminate these^{[citation needed]}; some became additional two-digit routes, while others became three-digit routes (see below). Only two pairs of these still exist: I-35 splits into I-35W and I-35E through both the Dallas-Fort Worth and the Minneapolis-St. Paul areas.

For the sake of efficiency, some Interstates coincide for various distances. This is usually referred to as a concurrency or overlap. One example is where I-75 and I-85 combine near downtown Atlanta to form the Downtown Connector, a major thoroughfare through the city. Another example is the merging and diverging of Interstates 90 and 94, which coincide and then separate several times across the upper Midwest and Great Plains. I-90 and I-94 even join with I-39 from Madison to Portage, Wisconsin, creating the longest triple concurrence in the Interstate Highway System.

Interstates 90 and 80 are concurrent for almost 280 miles in Indiana and Ohio. A recent addition is the I-73/I-74 concurrency, which runs along U.S. Route 220 between Asheboro and Rockingham, North Carolina. I-73 also will share routes with I-40 and I-85 on the Greensboro Urban Loop, a new bypass route around Greensboro, North Carolina. Strict adherence to the directional nature of the system results in some oddities. For a nine-mile (14 km) stretch east of Wytheville, Virginia, a driver can be traveling on both I-81 North and I-77 South at the same time (and vice versa) (see also wrong-way concurrency).

[edit] Auxiliary Interstates

See also: List of auxiliary Interstate Highways

Auxiliary Interstate highways are given three-digit route numbers, which consist of a single digit prefixed to the two-digit number of a primary Interstate highway, to designate spur or loop routes branching from either the primary route or one of its other auxiliary routes. A spur route is one that deviates from its parent and does not end at another Interstate (it is given an odd first digit); a loop route is one that returns to its parent (given an even first digit). The number given to the first digit of a route that branches from the parent to end at another Interstate depends on the state; some consider these routes spurs and assign odd first digits, while others consider them loop connectors and assign even first digits.

When letter-suffixed two-digit Interstates (see above) were abundant, their auxiliary routes were given a number without a letter suffix (with the exception of I-180N in Boise, Idaho, which is now Interstate 184).

Due to the large number of these routes, auxiliary route (a.k.a. "spur route") numbers may be repeated in different states along the mainline, but no two three-digit Interstates in the same state can share a number. For instance, I-90 in New York alone has a full set of three-digit Interstates: I-190, I-290, I-390, I-490, I-590, I-690, I-790, I-890 and I-990.

Closed loops usually retain a single designation for the entire route, even when they enter other states. For example, Cincinnati, like many other cities, features a large loop around the city that intersects with the primary routes I-71, I-74, and I-75 and travels through Ohio, Kentucky, and Indiana. The entire 84 mile (135 km) loop is labeled I-275. (It is also the only three-digit Interstate that passes through three states, with the possible exception of I-495, which briefly enters the District of Columbia, which is not a state).

The loop highway around Washington, D.C., known as the Capital Beltway, carries both I-95 and I-495. Originally, the loop carried only I-495, in anticipation of I-95 being routed through Washington, but in 1977^{[citation needed]}, I-95 was rerouted on the eastern half of the loop due to the cancellation of the segment that would have connected downtown Washington to College Park, Maryland, while I-495 remained on the western half. I-495 was added back to the eastern half of the loop in 1989^{[citation needed]}, creating a rare concurrency of primary and auxiliary routes.

Unlike primary Interstates, three-digit Interstates are signed as either east/west or north/south, depending on the general orientation of the route, without regard to the route number. For some looped Interstate routes, Inner and Outer banners are used as a directional labeling system as opposed to compass directions.

There are, however, exceptions to these guidelines:

• A contiguous loop surrounds the entire Minneapolis-St. Paul Metro area. I-94 intersects the loop in two spots and runs directly through it separating it into southern and northern halves; the southern half of it is labeled I-494 while the northern half of it is labeled I-694. The northern half rejoins I-94 approximately five miles before the southern half does; this stretch is signed I-94/I-694.
• I-270 and I-255 form a beltway around the greater St. Louis area. On its southwest corner, I-270 becomes I-255 as it crosses I-55 counter-clockwise only to terminate back at I-270 in the northeast. In the early 1980s, local residents stopped a plan to designate the entire closed loop as I-270 and renumber the stub of I-270 from Glen Carbon to Edwardsville to Interstate 870.^{[citation needed]}
• New York City has numerous spur routes from I-78 and I-95, but none of I-78's spur routes actually intersects with I-78. This is because I-78 was originally planned to continue east from its present terminus at the Holland Tunnel across Lower Manhattan, through Queens and across Long Island. This extension of I-78 was cancelled in the 1970s after I-278, I-478, I-678, and I-878 had already been established.
• An auxiliary route numbered I-238 connects San Leandro and Castro Valley, California, yet there is no I-38. Instead, I-238 carries the designation of the portion of State Route 238 that the Interstate designation replaced. I-238 could have been an auxiliary route of I-80, but at the time of I-238's designation, all child routes of I-80 (I-280 through I-980; I-180 was not used because of a Caltrans policy forbidding number duplications and the prior existence of State Route 180) were already designated in California.

[edit] Exceptions

A major exception to the overall numbering system is Interstate 99 in Pennsylvania, which was written into law as I-99 by Pennsylvania Congressman Bud Shuster; I-99 (which is also U.S. Route 220) is west of several Interstates that are numerically less than 99, but 99 was the nearest odd two-digit number available for the Interstate.

Other exceptions are I-82, which lies fully north of I-84 and is a relic from I-84 previously having the designation of I-80N; and I-39, which lies fully east of I-45 and I-49 but west of I-43

[edit] Other examples

The following two-digit Interstates change signed direction from their normal (even=east-west, odd=north-south) direction:

• 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 (3 km) in Nebraska before ending at I-80.

• I-64 east of Norfolk, Virginia after its intersection with I-264 becomes unsigned for directions as it loops around the southern side of Norfolk to the triple terminus of I-64, I-264, and I-664.

Two-digit Interstates in Hawaii, as well as the "paper" Interstates of Alaska and Puerto Rico, are numbered sequentially in order of funding, without regard to the rules on odd and even numbers.

Business Loop and Business Spur Interstates are not subject to any of the Interstate Highway standards. Their designation is simple: a business loop connects a downtown area with the parent route, while a business spur ends downtown (occasionally continuing from the end of the main Interstate). Business routes can split from either two- or three-digit Interstates, and can be repeated within a state. In a few cases, where an Interstate has been realigned, the old road has been designated a business loop because it is not up to standards.

[edit] Financing

About 56 percent^[13] of the construction and maintenance costs are funded through user fees, primarily gasoline taxes, collected by states and the federal government, and tolls collected on toll roads and bridges. The rest of the costs are borne by the federal budget. In the eastern United States, large sections of some Interstate highways planned or built prior to 1956 are operated as toll roads. The taxes dedicated to the construction and maintenance of highways are sometimes criticized as a direct subsidy from the government to promote and maintain automobile-oriented development.^{[attribution needed]}

As American suburbs expand, the costs incurred in maintaining freeway infrastructure have grown, leaving little in the way of funds for new Interstate construction.^[14] This has led to the proliferation of toll roads (turnpikes) as the new method of building limited-access highways in suburban areas. Also, some Interstates are being privately maintained (e.g., VMS maintains I-35 in Texas^{[citation needed]}) to meet rising costs of maintenance and allow state departments of transportation to focus on serving the fastest growing regions in their respective states.

It is possible that parts of the system will have to be tolled in the future to meet maintenance and expansion demands, as has been done with adding toll HOV/HOT lanes in certain cities such as San Diego, Salt Lake City, Minneapolis, Houston, Dallas, Atlanta^[15][16] and Washington, D.C.

[edit] The federal role in financing

The dominant role of the federal government in road finance has enabled it to achieve legislative goals that fall outside its power to regulate interstate commerce as enumerated in the federal Constitution. By threatening to withhold highway funds, the federal government has been able to stimulate state legislatures to pass a variety of laws. Although some object on the ground that this infringes on states' rights^{[attribution needed]}, the Supreme Court has upheld the practice as a permissible use of the Constitution's Commerce Clause.

The first major example was the introduction of the 55 mph (90 km/h) national speed limit in 1974. While its purpose was to save fuel in the wake of the 1973 energy crisis, federal speed controls stayed in effect for 21 years. The initial acceptance of the national speed limit emboldened various presidents and congresses to enact additional pieces of legislation, some of which have little to do with highways or transportation. Examples include:

• Increasing the legal drinking age to 21.^[17]
• Megan's Law legislation, requiring states to disclose identities of sex offenders.^{[citation needed]}
• Lowering the legal intoxication level to 0.08%.^{[citation needed]}
• Requiring the use of carpool (HOV) lanes.^{[citation needed]}

States also must meet minimum enforcement standards for all federally-mandated legislation (for example, minimum penalties for violation of these laws and a minimum number of per capita underage drinking convictions or a compelling explanation regarding why this number is not met).^{[citation needed]} This has proved to be controversial. Supporters hold that it is a way to provide an impetus to states to pass uniform legislation.^{[attribution needed]} Critics maintain that using highway dollars in this fashion upsets the balance between federal and states rights in favor of the federal government, and effectively withholds funds to leverage state governments into passing laws that would not have otherwise been introduced.^{[attribution needed]} Some have even argued that the current arrangement is unconstitutional.^{[attribution needed]} Law enforcement agencies in some states argue that efforts to meet quotas for underage drinking convictions have distracted them from other matters and strained relations with those under 21.^{[attribution needed][citation needed]} Any state that was to lose federal highway funding would quickly face deteriorating infrastructure, fiscal impoverishment, or both.^{[citation needed]}

However, a state that lost federal highway funding could theoretically threaten to stop maintaining its highways, if that were politically palatable to its residents.

[edit] Local maintenance

A few Interstates are maintained by local authorities:

• Baltimore, Maryland: Interstate 70 and Interstate 83 in the city limits^[18]
• New York City: Small portions of Interstate 278^[19]
• Washington, D.C.: As the city and District are identical, the District maintains the portions of Interstate 66, Interstate 295, Interstate 395 and Interstate 695 inside the city.

[edit] Chargeable and non-chargeable Interstate routes

Interstate highways financed with federal funds are known as "chargeable" Interstate routes, and are considered part of the 42,000 mile network of highways. Federal laws^[20] allow highways funded similarly to state and US highways to be signed as Interstates, if they meet the Interstate highway standards and are logical additions or connections to the System.^[21]

Called "non-chargeable" Interstate routes, these additions fall under two categories:

1. Routes that already meet Interstate standards. These may immediately be signed as Interstates once their proposed number is approved, or may be retained with a non-Interstate designation.
2. Routes not yet upgraded to Interstate standards. These cannot be signed as Interstates until they have been fully upgraded.

[edit] Signage

The majority of Interstates have exit numbers. All traffic signs and lane markings on the Interstates are supposed to be designed in compliance with the Manual on Uniform Traffic Control Devices (MUTCD). However, there are many local and regional variations in signage.

For many years, California was the only state that did not use an exit numbering system. It was granted an exemption in the 1950s due to having an already largely completed and signed highway system; at the time, placing exit number signage across the state was deemed too expensive. Since 2002, however, California has begun to incorporate exit numbers on all its freeways - Interstate, U.S., and state routes alike. To mitigate costs, a common occurrence is for Caltrans to install exit number signage only when a freeway or interchange is built, reconstructed, retrofitted, or repaired. The majority of the exits along Interstates 5, 10, and 80 now have exit number signage, particularly in rural areas.

In most states, the exit numbers correspond to the mileage markers on the Interstates (with an exception being I-19 in Arizona, whose length is measured in kilometers instead of miles). On even-numbered Interstates, mileage count increases to the east and decreases to the west (except on the I-90 portion of the New York State Thruway, I-90 between Chicago and Rockford, IL, the I-190 spur into O'Hare International Airport in Chicago, and the portion of I-76 in New Jersey, all of which count up going west); and on odd-numbered Interstates, mileage count increases to the north and decreases to the south and the exit numbers increase and decrease accordingly.

Many northeastern states label exit numbers sequentially, regardless of how many miles have passed between exits. States in which Interstate exits are still numbered sequentially are Connecticut, Delaware, Massachusetts, New Hampshire, New York, Rhode Island and Vermont. Maine, Virginia, Georgia, and Florida followed this system for a number of years, but recently converted to having the exit numbers correspond to mileage markers. The Pennsylvania Turnpike uses both the mile marker number and the sequential number. The mile marker number is used for signage, while the sequential number is used for numbering interchanges internally. The New Jersey Turnpike also has sequential numbering, but other Interstates within New Jersey generally use mile markers.

[edit] Interstate shield

Interstate Highways are signed by a number placed on a trademarked^[6] red, white and blue sign as shown to the right. In the original design, the state was listed above the highway number, but in many states, this area is now left blank. The sign usually measures 36-in (91 cm) high, and is 36-in wide for two-digit Interstates or 45-in (114 cm) for three-digit Interstates.^[22]

Interstate business loops and spurs use a special shield where the red and blue are replaced with green, the word BUSINESS appears instead of INTERSTATE, and the word SPUR or LOOP usually appears above the number. ^[23]

Over time the design of the Interstate shield has changed. In 1958, when the Interstate shield was introduced, the shield color was a dark navy blue and only 17-in (41 cm) wide.^[22] The MUTCD standards made a few revisions to the shield in the 1961, 1972, 1988, and 2000 editions. By 2000, the shield size nearly doubled, with some Interstate shields reaching 36-in in diameter.

[edit] Extremes

The most heavily traveled area of the Interstate Highway System is the 405 Freeway in Los Angeles, California, with a 2005 estimate of 382,000 vehicles a day.^[24] The least traveled section is Interstate 95 just north of Houlton, Maine (near the Canadian border), with 1,880 vehicles a day (2001 estimate).^[25]

The most extreme directional points of the Interstate Highway system are:

• Northernmost: The northern termini of Interstates 5, 15, and 29, crossing the Canadian border at the 49th parallel near, respectively, Blaine, Washington, Sweetgrass, Montana, and Pembina, North Dakota.
• Southernmost: A bend on Interstate H-1 in the Kaimuki section of Honolulu, Hawaii, less than half a mile (0.8 km) before its eastern terminus (lat. 21.3 deg. N.). The southernmost point in the 48 contiguous states is the southern terminus of Interstate 95 in Miami, Florida (lat. 25.8 deg. N.).
• Easternmost: The northern terminus of Interstate 95 near Houlton, Maine, at the border of New Brunswick in Canada (long. 67.8 deg. W.).
• Westernmost: The western terminus of Interstate H-1 in Kapolei, Hawaii (long. 158.06 deg. W.). The westernmost point in the contiguous states is a curve on Interstate 5 near Wolf Creek, Oregon (long. 123.23 deg. W.).

The highest point on the Interstate Highway System is at the Eisenhower Tunnel on Interstate 70 in the Rocky Mountains of Colorado, at the Continental Divide (elev. 11,158 feet (3401 m)). The lowest point on land is on Interstate 8 at the New River near Seeley, California (elev. -52 feet (-16 m)). The lowest point under water is on Interstate 95 in the Fort McHenry Tunnel under Baltimore Harbor in Baltimore, Maryland (elev. -107 feet (-32 m)).

The longest Interstate highway is Interstate 90, which runs 3099 miles (4 987 km) between Boston, Massachusetts and Seattle, Washington. The longest north-south Interstate highway is generally cited as Interstate 95; when completed, it will run 1927 mi (3 101 km) between Miami, Florida and the Canadian border (there is a gap in New Jersey). The shortest, albeit unsigned, Interstate is Interstate 878, a 0.7-mile (1.1 km) portion of New York State Route 878 adjacent to John F. Kennedy International Airport in Queens, New York. Another short unsigned Interstate is Interstate 110 near downtown El Paso, with length of 0.92 miles (1.5 km). The shortest signed Interstate is Interstate 375 in downtown Detroit, Michigan, at 1.06 miles (1.71 km).

[edit] References

[edit] See also

• Contraflow
• Gas tax
• Highway patrol
• Non-motorized vehicle access on freeways
• List of roads and highways
• Mile-log
• Parkway
• List of major freeway systems
• Adopt a Highway

[edit] External links

• Interstate Highway information
• FHWA Route Log and Finder List
• FHWA Turner-Fairbank Highway Research Center

da:Interstate Highway System de:Interstate Highway es:Red de Autopistas Interestatales de Estados Unidos eo:Interŝtata Ŝosea Sistemo fr:Interstate highway gl:Interstate Highway System it:Interstate Highway System nl:Interstate highway ja:州間高速道路 pl:Interstate Highway System simple:Interstate fi:Interstate Highway System sv:Interstate Highway System th:ระบบทางหลวงอินเตอร์สเตต yi:אינטערסטעיט הייוועי סיסטעם zh:州際公路系統